how to forget the passcode

I understand that you are referring to the passcode that is used to get to the Home Screen of your iPhone. I also understand that your iPhone has been disabled. You will have to reset the passcode to your iPhone by following the instructions in this guide published by Apple ➔  If you forgot the passcode or if your iPhone has been disabled. You will need a computer to execute this procedure and all the data on your iPhone will be erased.

Hopefully, you have a backup created on ➔ iCloud and/or on a computer. If you do then, you can ➔ Restore your iPhone from the backup file once your passcode has been reset and the iPhone has been returned to factory settings by the procedure in the link above.

Axel F.