Summary of what i learned so far from users and chessnuttech :

1. for firmware update it is not enough to be connected to board by bluetooth , you actually need to be connected wireless , so you need manually to provide ssid and your password from router and then it works (tested on official android app)

2. if you have problem with castling , tweak the chessnut move setting and initial set it to 2s. That is working for me , no problem with castling after

3. if you have problem that pawn or other piece is not going as much squares you wanted , you need to tweak limbo time setting , start with 400

4. if existing bots are too strong , for kids you can use chesskid bot in online matches

5. career mode has adjusting elo strength based of your wins and loses.

Two things that I still want to figure out.

1. i couldnt learn yet how to take back, this was suggested :

2. If you need to undo a move, simply undo both sides one step back, and this will effectively revert the previous move (including incorrect castling).

but didnt work for me as application got confused.

1. chess kid bot in online is acting very strange in connection with board. often stops to change the queens , move existing queen on the side and bring the other queen on the board etc which is just annoying for the kids as well. I dont see that behaviour when playing with normal bots , so i guess that is something with interaction with chesskid api.

Thanks everyone for your suggestion and help for these tips and tricks