Branch and HO are considered one and the same for VAT purposes. So there is no requirement for separate VAT registration for the Branch and Tax group cannot be created. You can amend the VAT registration of HO to add the branch license as well but same is not mandated by FTA.

Thanks Sajith and further What is treatment with Ajman Custom, should we link Ajman custom to FTA for import of goods.

If you have provided the Ajman Customs Code in your VAT application/registration details along with the letter from the Ajman Customs Authority, the Customs Code should ideally get automatically linked. If the same has not been submitted would recommend to use the 'Edit' option against your TRN on the portal to update the details.