One Lark Max transmitter won’t connect anymore

Hello,
one of my two Hollyland Lark Max transmitters won’t connect anymore — neither in the charging box nor by pairing through the RX.

I then tried to update the firmware. The TX unit that works did the upgrade without any problems. The faulty one seemed to do an upgrade too, but after connecting it to the PC, I either get a .bin file or sometimes an image file on the TX unit instead.

What can I do? Is there any way to do a full firmware reset just for the TX unit?

Thank you in advance for any help!