Your phone will automatically set up MMS when you insert your SIM card. You can also manually set up MMS on your phone manually, here's how:
From the home screen, swipe the arrow symbol up.
Tap Settings.
Tap Dual SIM & Mobile Network.
Tap a SIM card, such as, SIM1.
Tap Access Point Name.
Tap the plus symbol.
Under Name, enter Skinny Data
Under APN, enter wapaccess.co.nz
Under Username, leave blank.
Under Passcode, leave blank.
Under MMSC, enter http://mms.mmsaccess.co.nz/
Under MMS Proxy, enter 210.55.11.73
Under MMS Port, enter 80
Under MCC, enter 530
Under MNC, enter 05
Under Authentication Type, tick leave blank..
Tap APN Type.
Enter mms (note: in lower case) and Tap Save.
Tick MMS and Tap Save.
Tap Save.
To finish the process and activate the settings, you need to restart the device. Your phone will then be configured to use MMS.