When reassembling the phone, inspect the midframe and rear cover for any old adhesive seal. Make sure to completely remove any traces of it left behind.

Use 90%+ isopropyl alcohol on a Q-Tip, or the nearest equivalent available to you, to clean the adhesive residue off of the midframe and back cover.

Apply new Tesa tape or your adhesive of choice to the border of the midframe and border around the camera lens before installing the back cover onto the phone.