Placed a strip of washi tape at the edge back of an old iPhone case. This will be your basis for alignment. Then cut it leaving a small extra strip. Washi tapes are removable so you can adjust it anytime.
{2} Once your all done at the back side. Cut the extra edges of the washi tape.
{3} Once you’ve clean up the back side, do the same thing on the side part of the iPhone case. Cut a small portion of the washi tape on the curve part so you can fold it neatly.
{4} This part is optional. I can still see the print of the iPhone case so I doubled the washi tape. I just repeated step 2 and 3.