To delete a repository you can simply delete the lines conresponding and GitRoot will delete it.
Open .gitroot/repositories.yml
in the root repository:
1root:
2 defaultbranch: main
3 owners: []
4- repo1:
5- defaultbranch: main
Commit your change and push git add . && git commit -m "delete repo1 repository" && git push
. When the change will be in the defaultBranch GitRoot will delete it.