How can I edit my APN settings on Android 7.0?

[AC Question]

I use straight talk with my Verizon Droid Turbo 2. I have been using it for months with know problem. Until my OS updated. Since then I have had issues with network connectivity and mms in general. I cannot send group messages or multimedia. I tried to reset the apn settings and now it is the default Verizon Settings which are of course useless. There is no option to add a new network and all the settings input boxes are greyed out.. Any help would be great thanks.