Just twist the new battery cables with its equivalent on the board. Don't try unscrewing the board because there are 2 thin cables soldered to it, so it won't help that much.

A tool called "helping hands" can be useful here.

Don't forget about your thermal retractable sleeve/tube. Electric tape works too.

Once everything is soldered, cover the exposed metal and apply some heat so the thermal retractable retracts.