Set-up takes about two minutes. Do the steps in order.
Download it from f-droid.org and open the downloaded file to install. Choose Basic, not the full F-Droid app.
Scan this code with F-Droid, or open the link on the phone itself.

Find Indoor Cellular Survey in F-Droid and install it there. This matters: installing any other way permanently disables automatic updates on this phone.
In F-Droid, open Settings and make sure automatic updates are enabled. Security updates then install on their own.
Open the app and scan the code from your job brief to connect it.