HOW TO INSTALL CTGP-7 ON CITRA
1. Make sure you have a recent Citra version, for PC you will need Nightly 1823 or newer. The android version in the play store or third party builds may not have the plugin loader and not be compatible. To confirm your Citra is compatible, go to Citra Settings (Emulation -> Configure on PC or the gear icon on Android) then go to System and an option to enable the 3GX Plugin Loader should appear (no need to change it, only make sure it's there).
2. This is very important. You will need to
dump the Mario Kart 7 game AND the 1.2 update AS CIA FILES from your 3DS (See sections
Dumping a 3DS Game Cartridge to .CIA and
Dumping an Installed Title sections in
https://3ds.hacks.guide/dumping-titles-and-game-cartridges.html). After that, you will need to install them with File -> Install CIA on PC or the equivalent option on Android. If you don't do this CTGP-7 won't be able to find the game as it's not installed to the emulated 3DS.
Having the game as a .3ds file WILL NOT WORK. The game should be listed in the Installed games section and should have the 1.2 update icon, as you can see in the image below.
3. Download the CTGP-7 Installer .cia and install it with File -> Install CIA on PC or the equivalent option on Android. You can use the following link to get the latest version:
https://ctgp7.page.link/cia_downloader . Once it has finished installing, you can launch CTGP-7 by launching it from the Installed Titles section. If you want to access the CTGP-7 files for the MyStuff features, go to File -> Open Citra folder and go to the sdmc -> CTGP-7 folder.