Git commands to sync repo
To Add the old repo as a remote repository:
git remote add oldrepo https://github.com/path/to/oldrepo
2. To Get the old repo commits
git remote update
3. To examine the whole tree
git log --all --oneline --graph --decorate
4. To copy (cherry-pick) the commits from the old repo into your new local one
5. check your local repo is correct
6. send your new tree (repo state) to github
7. remove the now-unneeded reference to oldrepo
Video reference: