It depends.
You can reschedule your Session as long as you have:
1) available rescheduling quotas left, AND
2) the Course is not yet finished, AND
3) the Session you'd wish to reschedule has not past the Session expiry date yet.
When you reschedule such a Session, it will disappear but you will receive 1 extra Session quota for booking Sessions.
However, your rescheduling quotas will be reduced by 1.

Case 1:
Suppose you bought a 4-Session Course which started on 25 Mar 2025 and ends on 25 Apr 2025.
As per usual, for each 4-Session Course you book, you get 1 Rescheduling Quota, i.e. 1 chance to reschedule a Session.
Suppose you previously booked a Session for 21 Apr 2025 and you have not used your rescheduling quota yet.
Suppose that today's date is 20 Apr 2025 and your Session has not passed the expiry date yet.
You can still reschedule your Session but you must do so before the end date of the Course, in this case: before 25 Apr 2025.

Case 2:
You bought a Single-Session Course that has no rescheduling quotas on 25 Mar 2025.
As per usual with Single-session Courses, your Course will end on 25 Apr 2025 i.e. 1 month after the start date.
Today's date is 20 Apr 2025 and you booked a Session for 21 Apr 2025.
If you can't be present for this Session, you'll lose the Session because you don't have any rescheduling quotas.
You can still enter a message for the Teacher in the Session Notes of that Session explaining that you won't be able to attend and ask for notes or assignments. Your Teacher can see this, will understand and will provide the asked if possible.