Sir,
As per para 2 (iii) of Notification No.10/2020 – Central Tax dated 21st March, 2020 " who have registered Goods and Services Tax Identification Number (GSTIN) in the erstwhile Union territory of Daman and Diu and the erstwhile Union territory of Dadra and Nagar Haveli till the 25th day of January, 2019 have an option to transfer the balance of input tax credit (ITC) after the filing of the return for January, 2020, from the registered Goods and Services Tax Identification Number (GSTIN) in the erstwhile Union territory of Daman and Diu to the registered GSTIN in the new Union territory of Daman and Diu and Dadra and Nagar Haveli by following the procedure as below:-"
This clearly indicates that you have to take a new registration in the merged union territories by cancelling/surrending the old registration. You can transfer the ITC under old GSTIN to the new GSTIN as per the procedure prescribed in the above mentioned Notification.