Enable in Radiomaster TX16S - R9M ACCESS
See the source code and firmware releases in the repository https://github.com/cvetaevvitaliy/opentx
branch https://github.com/cvetaevvitaliy/opentx/tree/RadiomasterTX16S_ACCESS

Steps:

1. Flash modif FW for Radiomaster TX16S https://github.com/cvetaevvitaliy/Radiomaster_TX16S/raw/master/Firmware/Radiomaster_TX16S_R9M_ACCESS.bin
   for Jumper T16 https://github.com/cvetaevvitaliy/Radiomaster_TX16S/raw/master/Firmware/Jumper_T16_R9M_ACCESS.bin
   
2. Three wires need to be soldered, as shown in the picture