Hi Vijaya, welcome to the community.
Have you requested a demo account yet? If not you can do it from here: Get In Touch — Community Health Toolkit
After you get the credentials, enter the URL of the demo instance by selecting the Custom option that you get on the first screen when you open the app. Then you can enter the credentials.
If you have already selected option other than Custom and can’t get to the initial screen anymore, you can either reinstall the app or clear the storage from Android app settings.
Thanks,
-Binod