It would be good to perform this procedure while your resin tray is being cleaned, so that it is already out of the machine.
The membrane interface lip is pictured below. It is the part of the chassis that makes contact with the resin-tray membrane.
If the lip has dust, debris, or material on it, clean it with IPA and a nonabrasive cloth. Inspect the lip for any damage, as chips or cracks affect the tension of the resin-tray membrane during printing.