Excuse my ignorance, how would you do that? Do I post you my key?
Yes that’s right. Ideally a metal key although the little plastic service key can be used.
The lock has different wafers inside it, there are seven wafers inside, each has a different profile numbered 1,2 or 3. Put the key in th lock , see which wafers are sticking out, slide key out , remove the wafer that’s sticking out (they just slide out), check number, replace with a wafer that has a different number, slide key back in , if wafer is flush when the key is in the lock that wafer is done. Repeat as necessary until all the wafers are flush when the key is in the lock. I tend to leave the wafer nearest the keyhole out as I’ve found this one sometimes snags for no apparent reason and you can’t get the key out when refitting it.
There is a wafer in the end that is responsible for holding the lock into the pannier- leave this one out initially , put the key in the lock and slide the lock into the housing. Hold it in place and operate the lock to ensure the barrel turns etc and the key can be removed. When happy , slide the barrel out and fit the end wafer and refit the lock.
The process doesn’t involve any electronics.
It’s a five minute job, easy but a bit fiddly. Loads of tutorials on YouTube. Alternatively your dealer would do it for you, possibly for free depending on your relationship with them.
The lock I’m including has a selection of wafers to allow the lock to be matched to your key.