Please read the contract that defines the maintainer role in this project. In short:
If you want to check out pull request number 42 and you're comfortable running the code on your local device.
remote="https://code.03c8.net/krakenlabs/oasis.git"
git fetch "$remote"
git reset --hard $remote master
git pull "$remote" pull/42/head
npm ci && npm test && npm start
No need to add their fork as a remote.
Or for ultimate convenience (and github lock-in), use the github cli tool:
gh pr list
gh pr checkout 42