Can't push

I have not worked on a project for 10 months. Now I want to rework on it. I uploaded files to a new server, change the db connection. And I want to update the VCS (Git)

What I already done:

- Check for "remotes"

- Commit all changes

- Pull, Fetch from VCS.

What I have as error is:

"""Push version3a1 to origin/version3a1 was rejected by remote"""

I think I have changed the credentials for remote (gitlab) and now I have no idea how to update the credential. It may be so, or another problem.