On the associated RX there should be socket marked 'BIND' or possibly 'BIND/BATT'.
That's where you plug your 'lanyard
' in for the binding process.
It's only a shorting plug between the signal pin and ground which tells the RX to go in to binding mode.
Can you post the make and model number of your TX and RX please.
I may have the manuals in my archive.
But the binding process is essentially the same for all 2.4GHz sets.
It's necessary so that your RX knows the signature, and hence hopping sequence, of your TX and will only respond to that and no others. Cheers, Doug 😎