The 9xr has a socket in the bottom under the small rubber flap. Designed specifically for this ...
If you haven't done this before - then you MUST read up on it ... You will need to install Programming Application on your PC as well as download from GITHUB the relevant Firmware for your 9xr. Sites to look through : https://www.turnigy9xr.com/ https://code.google.com/archive/p/er9x/ https://github.com/MikeBland/mbtx http://www.er9x.com/ RCG has a long running thread that also within has information important that you need to know - so that you can flash FW etc. Sorry but you will need to scroll through it ..... you could PM "https://www.rcgroups.com/forums/member.php?u=327969" (JHSA) as he was a co-writer of the later er9x manual ... Your initial request - gave impression you already knew how to flash the 9xr ... but later seems you are starting at this. Take it slowly and read up all you can ... once you have it sorted - its not hard at all. Here are a couple of Youtubes : I know a lot use OpenTX .... but the foundation of that and also in my opinion the BEST FW for the 9x / 9xr ... is er9x .... (OpenTX has sided with FrSky and developed more for their radios).
I'll fly anything if I can launch it ! Youtube : solentlifeuk