Go to '3-dot menu'>Settings > IDENTIFICATION, and tap on the switch to turn the Caller ID on. You will see a pop-up.
In the pop-up message, tap GO. You will be navigated to your phone settings. Scroll down to the bottom of the page and tap on the “Choose apps”. In “Calling” section, select Truecaller as your caller ID app.
If after tapping GO you see a blank page, tap on the back button and you will see your phone settings page and then follow the above instructions.