I'm not sure to understand the question... whenever you have defined the Pick List (If it's a "Validation List" or a "Custom" one) you can go to the "Default Value" section and select "Value", you will have the very same dropdown than the users and can select the one you want (in this case, the first one):
Hope this will help, but if that's not what you needed, please explain a bit more.
To clarify, you want the first value of every pick list to be shown in the drop down - can you confirm if this is when the form is loaded or is it trigger based? It would be good to understand the use case as well on why you would want something you need the user to fill out to be auto populated with the first value...
I would like to set default value using first value from dropdown list in REQUEST OFFFERING. Below is my scenario:
1. Created a dropdown component using existing picklist/Validation List. I have checked "Auto-select if list has single value" option at picklist, however system doesn’t auto select the value even if there is only one value in selection list.
2. I can’t set the static value under Default value option in REQUEST OFFERING due to system populates the selection based on user login. Thus, different user might have different selection.
Notes: system should auto select the value when user loads the form.
To answer your original question on how to set up the pick list to auto select based on the first top value -- currently I can't find any setting to do this. Also, a note on the "Auto-select..." pick list setting - it only works for pick lists with constraints. However, you probably need to log an issue with support. That tick box works but only for object forms, doesn't look to be working for request offerings forms.
I hope this helps. It would still be good to get an understanding of the business requirement/use case you are trying to achieve here to see if a work around can be set in place.