How do I update my connection to nearby towers?

[KRYBUS58]

Several months ago I began dropping calls on routes I have traveled for years with no previous problems.  I live in metro Denver and have an Apple 6s plus.  I was recently told I could dial a number from my phone and it would update my connections with cell towers in my area.  Is this true or just and urban myth?

[Ann154 · Accepted solution]

The dial code for updating the Preferred Roaming List on the basic and 3G EDVO only devices isn't used on the 4G LTE devices. A simple reboot of the phone forces the phone to refresh its connection with the network and updates the preferred tower list.

[shultj2]

I have reconnected to the towers before 

This doesn't help me  I have rebooted numerous times

with no help 

[teeshot]

That or Airplane Mode on and off.  Only way.