If you cannot see your manager's name in the list, it means they have not registered yet or that they have registered but is still pending for validation. In that case, just select the option "I cannot find my Manager". You will be able to update that data later.

If your Manager is already validated and you still cannot find them, it may be linked to their job position (and especially the LCF associated). Thus, you cannot select a Manager who has a lower LCF than yours.