I’m assuming 2 scenarios and both meanings are given below:-
1- In the case if someone is inviting you to some event and also asking you to confirm about your intention the ‘confirm your presence’ means to confirm that whether you would be available at a certain event on a given time or not.
2- The other case would be if your are already present at an event and your host or organizer is asking you directly or on email or message to confirm your presence and you would reply present just like in the case of classroom when teacher ask you for the attendance.
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