Install F-Droid

Install F-Droid if you haven't already.

On old Android versions, you might need to enable the installation from "Unknown sources" in your System settings (usually under "Security").

Add the SpiritCroc F-Droid repo

You can find the SpiritCroc F-Droid repo here:

Check out this F-Droid tutorial for instructions on how to add it.

Install SchildiChat[f]

First, reload F-Droid's app information by swiping down F-Droid's overview screen.

Then, search for SchildiChat[f], or open this link using the F-Droid app. Finally, click install and that's it!