Safe Mode puts your phone in a diagnostic state (returned to default settings) so you can determine if a third-party app is causing your device to freeze, reset or run slow.
An alternate method is available if the device can be powered on and is responsive.
Ensure the device is powered off.
Press and hold the Power button (located on the top-right edge) until the Samsung logo appears then release.
Samsung logo appears approximately 10 seconds after "Samsung Galaxy Tab E" displays on-screen.
With the Samsung logo on screen, press and hold the Volume Down button (located next to the Power button).
Continue to hold the Volume Down button until Safe mode appears in the lower left of the screen then release.
This may take up to 45 seconds.