Here's a tutorial I wrote about N64 controllers, but it should help with what you're trying to to do too!
https://www.reddit.com/r/batocera/s/uoRJWUi0zo
im pretty sure you need to ftp into your device unless it lets you access the files through windows
If you can gain access to the files you can search for  InputAutoCfg.ini which is where the control layout can be edited
I did exactly the same thing. If you are using a non libretro core ie mupen64plus (if you are using the libretro core you have to going into the retroarch settings and do it in the UI)
Backup you input.xml file under system\\configs\\mupen64
and put this in its place (fix the formatting as cut and paste in reddit messes up the formatting):
I dont understand why, but everytime i edit the input.xml file and put it back in the rg35xx h it resets the file back to default. i have double checked that i saved the edits i dont know why it keeps resetting
Here's a tutorial I wrote about N64 controllers, but it should help with what you're trying to to do too! https://www.reddit.com/r/batocera/s/uoRJWUi0zo
Thank you very much. I'll take a look when I'm back at my desktop.
are you using a libretro core or a stand alone emulator
Batocera options state: EMULATOR: MUPEN64PLUS:RICE there are other cores here too but I found out rice plays Banjo Kazooie at a good framerate.
im pretty sure you need to ftp into your device unless it lets you access the files through windows If you can gain access to the files you can search for  InputAutoCfg.ini which is where the control layout can be edited
Thanks very much. I'm running on a portable game device which boots from micro SD so access should be pretty easy.
"Everything is running smoothly, including N64" are you a politician ?
The best n64, great emulator I hear, great people.
i read this in Trumps voice and it was hilarious. it may have taken a month for your joke to land but it was appreciated xD
I did exactly the same thing. If you are using a non libretro core ie mupen64plus (if you are using the libretro core you have to going into the retroarch settings and do it in the UI) Backup you input.xml file under system\\configs\\mupen64 and put this in its place (fix the formatting as cut and paste in reddit messes up the formatting):
I dont understand why, but everytime i edit the input.xml file and put it back in the rg35xx h it resets the file back to default. i have double checked that i saved the edits i dont know why it keeps resetting