I had to replace mine when the dealership I bought my car from broke it off right before I was supposed to pick the car up.
You unscrew the retaining nut and just pull the mast out. It has a long plastic thing connected to it that the motor reels in and out to make the mast go up and down. The plastic thing gets brittle with age and can break so if that has happened you'll have to remove the antenna assembly from inside the trunk and take it apart to get the old pieces out. @drew talks about this process in this thread and sometimes you get lucky and don't have to take it apart: https://www.nsxprime.com/threads/antenna-mast-replacement.83389/
An alternative option is to buy the S2000 antenna conversion from Mita, but that kit looks a little janky up close due to the way the conversion fitting is made.