Force a user to LDAP authentication

Goodmorning to all,
I have deployed on my farm a Turnkey Gitlab community edition appliance, about 9 month ago, during this period I have configured LDAP authentication : my problem is that I want to migrate one user from standard authentication to LDAP but I don’t know how to do that.

For example in openproject, on user account page, appear all authentication possibility (LDAP and standard) to choose : I expected that Gitlab has a similar way to do the job, but I don’t see any option.

Thanks in advance for your help