Go to Playstore and search for Gatewise.
Scroll down and look for "Join the Beta" section and then tap on "Join" option.
Joining Beta might take a while, but you may exit from playstore while waiting. It may take a few minutes to complete, make sure it says "You're a beta tester" before proceeding with the next step below.
Uninstall the Gatewise app from your phone and then have it reinstalled again. Check back in playstore to see if there is an Update option, tap on it.
You should now have the latest version 8.2.21 when you open the app.