To change your Master Password for Passwords Plus it is best to do it when you have all of your Password Plus enabled devices accessible.
Start by going to settings in Passwords Plus and choosing the “Change Master Password” option in the “Security” section. Type in your new password.
If you also use Passwords Plus on another device, the next step should be to open Passwords Plus on that device.
Because Passwords Plus has not yet synced your new Master Password onto your other device, when first prompted for your password you should type in the old password.
Once entering the old password, Passwords Plus will log in long enough to sync and then will again prompt you for your Master Password, which will be your new Master Password that you have just created.
If the old password does not work when entered into the new device, try the new password.
After this, your password has been fully reset and your new Master Password will be the only one that works with your devices.