Change the field to drop down

I have to change the highlighted filed as drop down filed. I am not able to find where is this filed loading from like which component, which class, which method and where to change.

Please can you give me direction where to start with.

this is the way i tried.

1. launch the application, right click on the Tiemsheet table , look for the the technical help.

2. Tried more field help, popup came up with no help documentation available.

3. Tried technical help.open a window with details.

4. Opened the WebDynpro component HRESS_C_CATS , from the package , PAOC_CATS_ESS_WDA

5. I am not able to find where this highlighted reason code is coming from to change the input field to drop down.

Thanks

Krish