GB wrote:

I thought maybe just join the correct pair of wires behind the switch
plate? What do you do with the spare one? Just jam it into a wago
connector so it's insulated?

yes, join the wires from COM and L1 in one wago, and isolate the
remaining wire from L2 in another wago, if that leaves the remaining
switch "upside down" swap L1 and L2

It's been wired in the normal way according to the wiki.

Whilst on the subject, is Adam okay? I haven't seen him posting recently.

Yes, I've just seem him on-site ...