For enabling change tracking on the entity. Steps below -
Please go to web.powerapps.com.
1. Settings icon on the right - > Advance Customizations
2. Customize - Open solution explorer
3. Left pane -> Components -> Entitties -> select your entity
4. General tab -> data services - Change tracking (enable it)
5. Press save button and then publish on the top pane.
PS : This (requirement to enable change tracking) is a workarround, we are working on fixing this limitation