You can apply to revoke a registered relationship.
You'll need to wait 90 days after you've applied before the relationship can be revoked.
You don't automatically get a certificate when your relationship is revoked. You can choose to get one at the same time as your application, or separately afterwards (see Get for a revocation certificate).
See Withdrawal of application to register or revoke a domestic relationship if you need to withdraw an application you have already submitted.