Login in your server with root access, then start ruby on rail consol and login.
Start Rubi consol using below command :
gitlab-rails console production
Wait until the console has loaded, you can search for email or username.
user = User.where(id: 1).first
user = User.find_by(email: 'email@example.com')
You can change your password from below commands :
user.password = 'secret_pass'
user.password_confirmation = 'secret_pass'
It’s important that you change both password and password_confirmation to make it work.
Don’t forget to save the changes.
Exit the console and try to login with your new password.