Secure a suction cup to the back cover, as close to the heated edge as possible, just under the Bixby button where the adhesive is thinnest.

The suction cup will not make a good seal on the curved portion of the glass, so avoid putting it on the very edge.

If the phone's back cover is cracked, the suction cup may not stick. Try lifting it with strong tape, or superglue the suction cup in place and allow it to cure so you can proceed.