OK, you need to log into Thomas Cook & go to the "Manage my booking" area, & add it there, or that's what's indicated. Without a booking ref, I can't check it for you sadly.
My friend also discovered that there were 2 levels of wheelchair assist & it seems that you, as she did, require assistance including ambulift, which takes you right up to the aircraft cabin.
When she got to Dalaman on Saturday night, she left her OH outside, in the drop off zone & went inside herself & brought the wheelchair + chappie to do the pushing back to him. No queuing anywhere, luggage virtually taken care of at both ends etc. One thing you will need is a fit to fly certificate, which is only valid for 3 days from issue, so if your flight is Monday, the earliest you can get it is Friday / Saturday. Her OH spent 5 days of their holiday in Esnaf, needing an op for a badly broken arm