Implement encoding and decoding on UHF=-RFID Card

I have an existing application which connects to read and write from a UHF reader. users will use the UHF cards to login to the application. the code to connect the reader is already done and we are getting data from the card in Hex format i need an RFID expert to help with encoding,writing and Decoding Phone number and user Id into the UHF/RFID cards instead of just the HEX numbers