Is there anyway I can restore a user's Calendar to an earlier date?

Here is what happened, the employee was trying to merge a calendar into his iPhone. It wasn't working with his iPhone calendar so he decided to give the GroupWise calendar a try. It merged but it went horribly wrong and created 10-15 appointments everyday for the next ?? years (some are legit and some are just characters for the subject). What I'm trying to do is find a way to restore his calendar to the day before he did this merge but I cannot seem to find a way to do this.

Anybody have a suggestion for me? Is this even possible?

Thank You