#stiches

The Metkayina healers were busy caring for their own injured people and likely wouldn’t prioritize a human (against whom they had just fought). Plus they don’t know human anatomy.

It had to be someone with actual medical knowledge, so Lo’ak and Tuk are out.

Neytiri caused the wound and was occupied preparing Neteyam’s funeral (it's already stitched by then).

Jake was with Neteyam too. His own facial cut is stitched up and he couldn't have done that himself, so there must've been a second person who can stich someone up.

This leaves Kiri. As tsakarem, she has the med knowledge. She's the one caring for Spider's stripes and hair all the time, so she must know how to care for his human body in a medical sense too.

They were so happy to have each other back and can't stop touching anyway...

Extra thoughts: