Variable Contains the Name of a Field in a Record

In a Variable is a Field Name
This is tough to explain because you have to understand teen age suicide.
The Varable HoldFld Contains the Name of a Field in a Record
Example the Contents of HoldFld could contain BullyX
In the Field BullyX I want to insert a diasnostic Number.
I have tried all kinds of syntax, but I just do not know what the page wants.
In the Law Enforcement file Scd has the diagnostic code, for the purpose of argument the code will be 553693
I want the field BullyX to contain 553693 on the teenager's reason for death by officer. 

Does anyone know how to do this?

Thanks in advance

Tony