Hello Venkatajalapathy P,
Mendix created quite some documentation for using a native app offline check the documentation here:
Offline first:
https://docs.mendix.com/refguide/mobile/building-efficient-mobile-apps/offlinefirst-data/
To test your application you can create the application and put it in your mobile device and then you can for example switch to airplane mode, also you can use an emulator for example bluestack, however this is less accurate.
More here:
https://docs.mendix.com/refguide/mobile/distributing-mobile-apps/
Be aware that you need to synchronize data between the application database and the device database and that your logic that you execute offline can only be device side.
Hope this helps,
Good luck