When to make changed between Training, Quali and Race

F1 25 is my first F1 game and I am just getting more into setups during career mode.
I have read to use older engine parts during training and change them for quali and races.
But when to exactly change them? Changing engine parts take time, and I am not allowed to make major changes at some point because of parc ferme rules.
Same question for setups. Once I am at the day of race, I can’t get into the setup settings at all.
So when and where do I do the changes?