If you have screen vise clamps, you can work around the camera bar. Secure the clamps to the perimeter of the device.

Apply tape to the perimeter of your rear glass to protect its finish.

Place coins or similarly thick objects along the edges of the rear glass. Make sure they're as thick or thicker than the camera bar.

Stack multiple books or other heavy objects on your phone. Leave them in place for thirty minutes or longer. Ideally, leave them stacked overnight.