When you get to the page click Continue, then CUSTOM APN
Select Your Country and then the carrier you want to use, click done, create profile
A window will pop up on your phone, click install then done.
Tip: On Step 3 sometimes you will be provided with multiple versions of you carrier, choose the options that is matches your plan. For Example if you have 4G on AT&T you would need to scroll down and select “AT&T (HPSA+)