If you are having a registered office or any business in DTA and Second unit is in SEZ or only unit in SEZ then following can be done.
If you are having One unit in DTA and another in SEZ then you are required to take separate registration for SEZ, in terms of 1st Proviso to Rule 8 of CGST RULES,2017. In either case please refer FAQ of Registration for SEZ Q.no.3 and you may also visit your jurisdictional office for assistance.