dmd docs
How do I perform a full app reset?
Close DMD2 and clear its app storage. That erases everything and puts the app back to how it was on first run.
Go to Android Settings → Apps, tap DMD2, then Storage & Cache, and clear the storage. You can also press and hold the DMD2 shortcut and choose App Info → Storage & Cache.
Clearing app storage is not the same as uninstalling and reinstalling. An uninstall often leaves files and settings behind, which is exactly what you are trying to get rid of, so use clear storage.
Before you do it: if you have a license, sign in to the DMD HUB and let a sync finish, so your profiles, GPX and locations come back afterwards. Export anything you keep only on the device. And expect to download your offline maps again.
Cannot close DMD2? Use Shutdown in the Quick Menu — see the answer on exiting the app.