How to call S7-300 function block

Front fork function blocks in the data reference is not called if they are able to call what should call

The best answer
Front fork features may indeed have not been called, or be called indirectly.
Indirect calls, such as UC FC [#TEMP3] depending on the #TEMP3 value calls different FC.
If it does not call directly in ladder diagrams can be added to the program.