Here’s my translation (2^nd attempt)

Alan

From last week, I belatedly worked out that röktust is past tense reflexive form of rekja, but I guess you all knew that.

Stígandi neytti þá íþróttar sinnar, ok var lengi í framkrókum með þeim áðr enn hann gat náð henni. 
Stígandi then made-use-of his skills, and (it) was a long time in exertion between them (Stígandi and the filly, ie they contended with each other for a long time) before he was-able to get-hold-of her (the filly).

Vildi hon þá bæði bíta ok berja. 
She wanted then both to bite and smite.

En hann gjörði henni orkumun svá at hon gat hvárki gjört. 
But he rendered a difference-in-strength (orka + munr) with her (ie he used  his superior strength) so that she was-able to do neither( ie bite or smite)

Komu þeir nú til þeira Knútr ok Hörðr. 
They, Knútr and Hörðr, came now towards them.

Ok sáði Knútr yfir hana úr posa kerlingar. 
And Knútr scattered over her (dust) out of (the) little-bag of (the) old-woman.

Fell hon þá niðr sem dauð væri.
She then fell down as-if (she) were dead.

Síðan tóku þeir tal með sér hversu þeir skulu með fara. 
After-that they took to conversation among themselves how they shall manage (it, the situation, fara með e-t, Z18)

Ok kom þeim þat ásamt at sá skyldi fyrst heim koma er fyrst fór heiman. 
And that came together for them (ie they agreed) that that-one (ie he) should come back (lit: home (ie to the maiden-king´s court)) first who first journeyed away (lit: from home).

Fara nú síðan þott þeir væri stirðir af sárum ok kreistingum er tröllin höfðu þeim veitt. 
(They) journey after-that although (var of þótt) they were stiff from (the) wounds and squeezings which the-trolls (neut plural) had given them.

En þá er þeir komu þar sem vegir þeira skildust, þá skildu þeir flokka sína þvíat úr sinni átt átti hverr þeira at koma. 
But (And) then when they came there where their ways parted, then they separated their herds because each of them had (ie was obliged) to come out-of his-own quarter (ie direction).

En þat ætlaði meykonungrinn at þeir mundu eigi fundist hafa.
But (and) the-maiden-king expected that, that they (ie Knútr, Hörðr and Stígandi) would not have met-one-another (ie during their respective trials).

Svá er sagt at Stígandi kom fyrst heim ok var þá sól í landsuðri er hann kom. 
So (it) is said that Stígandi came back (home) first and then (the) sun was in (the)-south-east when he came.

Meykonungrinn var þá í nýklæddr. 
The-maiden-king was then in, just-dressed (as in recently, not barely 😊).

Stígandi rak svínin inn í skíðgarðinn þar sem meykonungrinn var fyrir. 
Stígandi drove the-swine inside into the wooden-fence(d) enclosure) there where the-maiden-king was stationed (already)

Hann kvaddi eigi meykonunginn, en kastaði inni mögru gyltinni niðr fyrir fætr henni. 
He greeted not the-maiden-king, but cast inside (the) lean young-sow down before her feet.

Ok bað hana at hyggja hvárt at ómeidd væri. 
And (he) bade her to guess (judge) whether that (the sow) was uninjured.

hon sagði at hann hefði mannliga efnt sína sendiferð. 
She said that he had manfully fulfilled his errand.

“Hefir þú fram lagit slíkt sem þú hefr meðferðar?” 
“Have you placed forward (ie delivered up) such as you have in your keeping (see meðferð, Z2).

Hann tók höfuðit Hjálms úr serk sér ok snaraði fyrir brjóst henni. 
He took the-head of Hjálmr out of his shirt and flung (snara, Z4) it) against her breast.

Menn gripu til vopna. 
Men (Folk) grapped for (their) weapons.

Hon bað þá kyrra vera. 
She bade them to be still (calm)

“Eigi skal þessa hefna.” 
“(one) shall not avenge this (genitive neut sg – hefna + gen).”

Stígandi sá at hreyfðist gyltan in magra. 
Stígandi saw that the-young sow, the lean (one), stirred.

Meykongurinn hljóp þá at ok greip í burstina ok snaraði til Stígandi, en hann greip við ok sneri í burtu. 
The-maiden-king ran then to (the sow) and gripped into the-bristles (of the sow) and flung (snara, Z4) (the sow complete with bristles?) towards Stígandi, but (and) he gripped against (the bristles?) and twisted (snúa, Z4) (the bristles and skin?) away. (highly confusing – any sense that I can make of this comes from what happens next)

Sáu menn þá at þar lá kona fögr sem hamrinn hafði verit. 
Folk (men) saw then that a beautiful woman lay there where the-skin had been.

Meykonungrinn lét næra hana. 
The-maiden-king caused to nourish (noera) her (ie had her fed).

Stígandi brenndi svínshaminn.
Stígandi burned the swine-skin.

En litlu síðar kom Hörðr með hrossin ok kastaði flókafolaldinu fyrir fætr henni ok bað hana at hyggja hvárt nökkut væri af hans völdum meitt. 
But (And) a little-later Hörðr came with the-horses, and cast the filly-foal-with-the-matted-coat before her feet and bade her to guess (judge) whether anything were injured of his doing (vald, Z3).

Hon sagðist þat eigi sjá en spurði hvat hann vissi til Knúts.
She said-of-herself not to see that but (and) asked what he knew with-respect-to Knútr.