I would first seek to have the other party agree to set aside your stipulation. However, if that stipulation resulted in any type of order by the Court, you might have to file a motion to vacate the prior Stipiulation and Order, and set the matter in question for hearing.
Has the stipulation been entered into an Order with the Court? If so, then you will need to file a motion to vacate the stipulation and order. If not, then I recommend that you contact the opposing counsel (though your counsel) and request that the stipulation be set aside. Good luck to you.