BetterDiscord is not showing in the settings
Firstly, reinstall BetterDiscord with the most recent version of the installer available at BetterDiscord's official site (opens in a new tab).
If the problem persists, proceed with the steps outlined below.
This answer will work for Windows users only.
Stop Discord
Quit discord using task manager or the system tray (opens in a new tab) icon.
Go to appdata folder
Open Run (⊞ Win + R), type %localappdata/%, and then press Enter ↩.
Delete folder
Navigate to the Discord folder, and delete the folder inside named app-1.0.9005. If there is no such folder, or if it is named differently (e.g app-1.0.9004), delete it reguardless.
Restart PC
Restart your PC and relaunch Discord. It might throw an error at you, just ignore that and continue with the guide.
Install BetterDiscord
Download and install BetterDiscord. The installer can be found at BetterDiscord's official site (opens in a new tab).
Restart Discord
Restart Discord by quitting it from the task manager or the system tray (opens in a new tab) icon, and launching it again.
If none of the steps mentioned above work, as a last resort you could try reinstalling Discord (opens in a new tab) and BetterDiscord (opens in a new tab) from scratch.