Go to the App Store (iOS) or Google Play Store (Android), search for Microsoft Dynamics 365 Business Central.
Google Play Store: https://play.google.com/store/apps/details?id=com.microsoft.dynamics.ProjectMadeira&hl=en_ZA&gl=US
Apple App Store: https://apps.apple.com/us/app/dynamics-365-business-central/id1093325047
After completing the installation, follow the below steps to get connected to BC:
Run the app, then select "Advanced Options"
Insert your Service Name (the URL that you normally use to log into BC), then tap the right pointing arrow to continue
Insert your username and password, tap the right pointing arrow to log in.
Once logged in, you can then use BC