Liquid zest plus

Option 1 which may work.

Go to android device manager: https://www.google.com/android/devicemanager

Log in using the main account you used to set up your phone.

Once you log in, if you phone is connected to wifi, or cell data, you will see it.  You can then try this:

1. Find your T08 on the screen
2. Enable “Lock & Erase” feature
3. Then follow the given steps on the page to lock your phone (don't click erase by accident)
4. Set a temporary password
5. Enter the temporary password on your T08 to unlock it.
6. Create a new password

The above method assumes phone is still accessible on some network.

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Only other thing you can do, is a factory reset.  In older versions of android it used to give you the option to reset password after 5 times wrong password, via your associated google account, but I don't see it in marshmallow.

Do do a factory reset, you need to boot the phone to recovery mode, and then do a factory reset from there.

1. Switch off the phone, and wait for it to be completely off.  
2. After that, press and hold together the Volume Up + Power button for several seconds
3. You should release held keys when the Boot Mode appears.
4. Then from the menu on the screen select option Recovery, by using Volume Up to scroll and Volume Down key to confirm.
5. When an Android Image displays on the screen press the Power button to enter Recovery Mode.
6. Use Volume Down to choose "wipe data/factory reset", and then push the Power button to confirm.
7. Select "Yes--delete all user data". Use Volume buttons to scroll and Power rocker to choose.
8. To restart the tablet, select "reboot system now".

You can see the prcesdure here: http://www.hardreset.info/devices/acer/acer-liquid-zest-plus-z628/

Scroll down to Method 2.

Keep in mind this will delete all your info.

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Good luck