[Using Affinity Photo (2) as external editor in old version of Lightroom]

I use Lightroom 5.7 (not prepared to pay subscription) as my DAM. I have it set up so if I wish to edit, I can right click (windows) and open Affinity Photo (V1) to edit. I want to change this to Affinity Photo V2 but can't work out how - I guess it is because when I bought it, it was delvered to my PC in a different format.  Any ideas on what I can do to fix this?

Thanks

Garry