How to stop a user from adding into a field

Correct normally in a drop down list there is a a checkbox when I create the drop down list in that form. This field is coming from another table. 

In the child table on the field that it is sharing to the parent table - it has these options

The field says 

I have picked User input because from another field won't work - from list gives me a drop down list option for me to add the choice but I have used a report on the form with the choices. Does this make sense? It didn't happen on the legacy forms - 

I have a form with a field from another table. "Location table has many tours" this brings the field that I want to my "Tours table"  That field from the child table is a multiple choice. On the form I use a default record picker that gives the value of the list in the child table. It is a pull down menu with choice.

Normally in the field there is a choice to allow users to create a new choice. On the old legacy forms - on the new forms it allows them a choice. IT never did this before. 

Because this field is from a child table and i go into the field from build form - it has no such choice. Because it is a text Look up field from the child table. Refrernce field comes from a different table. when I edit the relationship there is no where that I says DONT let people create location. 

When I go into the field in the child table it is a text field. Under text field options I have User input which I have checked off

From list and then it wants me to add data to this list and then it has From another field - 

I don't know maybe I am not explaining it correctly with all the right terminology. 

Yes that worked - thanks - Not sure why it can not be done in the field but I tested and it worked - thank you  for all your patience