Turn off your Telefunken Tel-90
Press and hold both Volume up and the Power button until it turns on' See other combinations here http://satechhelp.co.za/3548/Access-Android-Recovery-Virtually-Android-Smartphones-Tablets
If you come across the "No command" mode then try the following to bypass it to recovery mode:
Tap the Power key
Tap the Volume down or up
Tap the Volume down/up together with the Power key
Scroll to 'Wipe data/ factory restore' (scroll with Volume Down)
Confirm selection with the Power button
Scroll to 'Yes---delete all user data'
Again, confirm with the Power button
Wait until you see Wiping complete
Short press the Power button to 'Reboot now'.