Unlock android pattern after changing Gmail Password
On older Android devices, if you lock your phone using Google's find my device you'll be able to choose a new password, and you'll then be able to access your phone.

Go to android.com/devicemanager enter your email address and password. Now, press on lock. You will now see an option to put in a password to lock your phone with. After filling it out and pressing lock, You should be able to unlock your device with the password you chose.