Using the guitar pick, unclip the back cover. Quite difficult on newer model, use more than one pick.

Easier way to go in is to slide in between volume and power button. This is the softest part of the back cover. The first clip is just a bit further up to the volume + button. So gently lift up to release the first one. You will maybe break one or two bigger clips. But it will clip back just fine with the smaller clips.

Otherwise, buy a replacement back cover before. Use guitar pick push the cover away from the frame to avoid breaking bigger clips while closing back.

Unclip both upper and lower part to get lower part easily out. Check out the back cover photo to identify the clip position.