Bad battery cell & won't connect to app.

Hi everyone,
I recently purchased a Carbon GT board. It doesn't seem to work right. It cuts out and turns off power to the board when you try to accelerate hard, either kicks into safe mode or trips power switch to off. I've checked a lot of the connections, and all are ok. It appears that one of the Battery cells is bad, causing the issue, I believe. Looks like Cell 6 is the issue.? See picture attached.
I also cannot connect my board to the Evolve app. I can connect my board to the remote with no issues. Any advise on what i can do to repair or replace the battery cell, or battery. Also any ideas how to get it to connect to the app? Any help or advice would be appreciated. Thank You.