$ cd gitdir/repo

$ git remote -v
origin https://git.example.com/project/repo.git (fetch)
origin https://git.example.com/project/repo.git (push)

$ git remote set-url origin https://username@git.example.com/project/repo.git

$ git remote -v
origin https://username@git.example.com/project/repo.git (fetch)
origin https://username@git.example.com/project/repo.git (push)