Battery accidentally disconnected needs reconnecting

I’m not sure I 100% understand what you mean with “tab” but if you are referring to the female connector that is soldered down on the board (meaning the part on the left in step 3 of the battery replacement and not the part they are pulling out with the tab) I’m afraid you’ll have to order a new connector and solder it in place, but you’ll need to double check that none of the soldering pads are ripped off the board, otherwise you’ll need to use jumper wires to restore the connections. Maybe it’s better to take it into a repair shop to have them have a look at it since you mentioned one of your hands shakes a bit too much.

If you didn’t break off the connector of the board, just try to slide the male end of the connector back into the female connector that is on the board like mentioned in Step 3.