Two trade name same pan, same state, nature or business is also same

Please clarify about If a person (Individual-Proprietorship) operate a business with two Trade Name having same Pan in same State, same-Circle(District or Place), nature of business is also same, and he migrated from VAT to GST Regime, How they add both Trade Name in one GST Reg. Certificate. 
For Eg.-
One of My Dealer who Engaged in Earlier Fertilizers Business, Trade Name- MOHIT ENTERPRISES since 10 year ago and also registered under VAT Act , and they migrated in GST Regime in Dec'2016 and the successfully got GST Id/password..But Now they need to ADD another Trade Name IFFDC Krishak Seva Kendra, Commodity Dealt- Fertilizers,
(This name in Mandatory Suggest by IFFCO Company) 
So, How they got both Trade Name in one GST Reg. Certificate
Kindly help us in this situation, More than 100 dealers having same problem, some one is new registrant, having two trade name
Kindly provide us solution as soon as possible.