Advanced upset handling is just that its more about getting comfortable with an out of shape aircraft so you can quickly identify what is happening and rectify it
This is very good advice Jjoe - flying normally afterwards will rapidly become easier too, lowering your workload.
All I'd add is pick wisely! Please don't be seduced by doing such training in an inappropriately punchy machine (e.g., XA-42, Extra
300, Su29) as while all three are incredible they're
very expensive.
Do it in a Pitts / Firefly / Bulldog type machine with a guru next to you / behind you.
Alan Cassidy at White Waltham is excellent, Cambridge aero club has a good rep, as do Ultimate High. I think Charlie Kimbell is around the Midlands and he is also excellent.
https://www.aerobatics.org.uk/training/directory is a useful resource.