If your Mudita Kompakt is stuck in a loop when it starts up, you need to perform a factory reset.
This process will erase all data on the phone, so please be aware that any information not backed up will be lost.
Factory reset procedure:
Power off the phone
Hold Power and + Volume Up buttons together until you see the "Select Boot Mode" screen
Use the Volume Up button to scroll to "Recovery Mode", then click the Volume Down button to press "OK"
Once the screen shows a broken robot icon, press and hold the Power button, then click the Volume Up button once to open the Recovery menu
Use the Volume Up/Down buttons to scroll to "Wipe data/factory reset" and click the Power button to confirm
Wait for the factory reset to complete