Push change to pull-request branch

Hi, does anyone know how I can push to a pull-request branch? The workflow I’m after is someone creates a version number and my job generates some hashes that are committed back to the contributor’s branch to be included in the final merge. Can someone help me figure out how to write that step?

If you’re the repo admin PR branches by default “allow edits by maintainers”.

Just need the fork added as a remote and you can push to the PR branch. (Or well a GitHub action workflow could using a PAT I guess.)