Sorry, you're right GG. If you've forked the official Roll20 sheet repo, and downloaded it on your PC with the github application (or direct git commands) some time ago, and want to put your own modifcations in it on a specific sheet, and then make pull request, you'll have to update your fork first, to catch up with the current state of the official repo, to push only what's different (=your modifications). So before putting your modified files locally in your fork, update it with the commands above, push to your repo on github (so your fork is up to date locally and on github) and then put your modified files and make a PR. This avoids to have to delete and refork, and/or to push unwanted modifcations from other/older sheets (and have merge conflicts like I see sometimes happening). There's perhaps a better way, but that's I've been using for years.