Standard bind procedure.
Using your favourite method (configurator button / cli
bind_rxcommand / physical button on the board / setting
expresslrs_uid = 0, saving and rebooting the board) put the rx into bind mode. Enter elrs lua in your handset and press the bind button. RX and TX should be now bound. Please mind the order, RX first, TX second. How to bind tutorial (thanks to @JyeSmith ): https://www.youtube.com/watch?v=U2sxqx2oT4k