Manual Roam iOS 9.3.1

I've recently purchased a refurbished iPhone 6 64g and taken out a sim-only contract. The settings don't seem to work and the phone is constantly searching for signal. I have tried resetting factory settings, cleaning the sim and re-downloading the network information but nothing has worked so the carrier has told me to do a manual roam. In iOS 9.3.1 the options on the 'settings' menu have changed and there isn't the choice to select 'cellular' or 'mobile'. Is there another way to do a manual roam?