First of all, I would not make any changes directly in the "main" repo. If you really want to have a "main" repo, then you should only push to it, never change it directly.
Regarding the error you are getting, have you tried git pull
from your local repo, and then git push
to the main repo? What you are currently doing (if I understood it well) is forcing the push and then losing your changes in the "main" repo. You should merge the changes locally first.