Open this page on your phone and tap the download button.
Open the downloaded file. Android will ask you to allow your browser to install apps: allow it, then go back and tap "Install".
Open Kelesh Tracker. When the first update is available, the app asks to be allowed to install apps — allow it, and later updates install automatically.
If you have an older Kelesh Tracker from Google Play, this is a separate app; you can uninstall the old one.