> þó hefi eg nú gervan (pp agreeing with direct object, sáttan, f sg) þig sáttan við Njál og sonu hans
> still I have now made a settlement for you with Njál and his sons

gervan ... sáttan: both masculine accusative singular, I think, agreeing with the direct object þik.  "I have made you (sg.) settled" (i.e. I have arranged/concluded a settlement between you and Njáll).  If he was saying "I have made a settlement for you," I would have expected "you" to be in the (benefactive) dative.

The adjective görr (gørr, gerr) came to be used as a past participle for the related verb gøra (gera), although the true past participle gørðr  also occurs.  görr "skilled, ready, done" introduces a -v- before vowels in inflections.  Feminine accusative singular would be gørva (gerva).

Normally in prose, past participles of verbs that form the perfect tense with hafa just take the nom./acc. neuter inflection, which some grammar books call the "supine" when it's used in this way: er ek hefi þik fundit "in that I have found you" (Svarfdoela saga 28); er ek hefi þik hér ratat "that I have found you here" (Laxdoela saga 63); at ek hefi drepit skógarmenn þína "that I have killed your outlaws" (Bjarnar saga Hítdoelakappa 22); er ek hefi hann á mannfundum sét "when I have seen him in public" (Laxdoela saga 40).

But sometimes, especially in earlier texts and old poetry, hafa is used with a past participle which is inflected to agree with the direct object, as here.  There's an example of this in the second strophe of Völuspá:

þá er forðum mik
foedda höfðu;


"[I remember the giants born of old] who reared me long ago" (foedda = feminine accusative singular).

LN