Upvote:12
Briefly, you checked 'no' on a sensitive field. It's a bad situation and in the archives here we have one or two 10 year bans from doing that. Everybody makes up some excuse like they forgot or they were absent-minded or whatever. The point being that Entry Clearance Officers do not react favourably to excuses, instead they refuse (and possibly ban the applicant).
Your payment has already cleared so it's too late to tell the bank to block it. Blocking the payment is the 'golden solution'.
You are at the biometric enrolment stage. At that stage the application is 'frozen' into their database and there's nothing you can do about it.
Also at that stage, the applicant prints out the application and enrols their biometrics at one of UKVI's commercial partners.
You will have to make a pen and ink correction to your application. They will permit a small change to a single item. So cross out the 'no' and check the 'yes' and then add the date and other reference info.
Since the ECO works entirely off of Proviso and very rarely sees the paper application (or anything paper for that matter), you will need to tell the VFS to mark your application as 'modified'. When it gets to the mail room they can enter the change into Proviso and the ECO will not get you for deception.