First, change your key password in Mailvelope. Then create a new recovery document to use the your new key password on other devices.
Open your browser with the installed Mailvelope-addon and follow these steps:
Create a recovery document to be able to restore lost encryption data and to use Encrypted Communication on other devices.
Keep your recovery document in a safe place for future reference.
If you changed your key password in Mailvelope on your computer, you have to synchronize your GMX Mail App for Android with the new password.