You go to VFS , you colour copy every page of your old passport, fill in the forms , when your new passport returns to VFS you go in hand them your old passport the corner gets cuts off and you leave with both
Here of a lot getting turned around on a 60 day exempt and sent back at their own expense to the last port of boarding. Everything is Evisa so you won’t be getting back in 5 days
MUST be done at the UK Embassy in Bangkok you will need your actual divorce certificate if previously married and if your former wife passed away the death certificate. You will also need a copy of your wife to be ID card.