Remove your suction handle from the rear glass.

Slowly open your iPhone by swinging the rear glass up from the left side, like the back cover of a book.

Be careful not to strain the short charging coil flex cable.

Lean the rear glass against something to keep it propped up while you're working on the phone.

If you don't have anything at hand to lean the rear glass against, your suction handle can do the trick.

During reassembly, lay the rear glass in position, align the clips along the top edge, and carefully press the top edge into place before snapping the rest down. If it doesn't click easily into place, check the condition of the clips around the perimeter of the rear glass and make sure they aren't bent.