Aruino BT problems

hello guys
A few days ago I set my arduino BT to MUX mode, then the arduino BT can not upload anything, so I use another arduino board, and the "arduino as isp" method to burn program to my arduino BT, but it still can not disable the MUX mode, and if I don't use an extra arduino board(as AVR-ISP) I can not upload anything.
does someone have ideas?
Thanks :cold_sweat:

...NO response... :astonished: