Download and install Termux from: Termux | F-Droid - Free and Open Source Android App Repository
Download and install Termux:Widget from:
Termux:Widget | F-Droid - Free and Open Source Android App Repository
Open Termux and run this command:
pkg upgrade -y && pkg install wget unzip -y && mkdir temp && cd temp && wget https://raw.githubusercontent.com/TGP17/citra-android-update/master/setup-script.sh && cd … && mv ./temp/setup-script.sh ./ && rm -rf temp && chmod a+x setup-script.sh && ./setup-script.sh`
You also might need to grant Termux the permission to manage storage and to display over other applications on some Android Skins. These can be granted from the System Settings.
Now go to your home screen and add the widget with the Termux icon from Termux:Widget and select either the
citra-nightly-update.sh and repeat for the other one if you want to have a shortcut for both.
Now if you click one of these Shortcuts, Termux will open and after a few seconds, will prompt you to update Citra.