The issue here is that the user wanted to pre-populate their post custom fields on their frontend form with their current user's custom field so they won't have to re-enter the data.
Solution:
You can pass the shortcode for that user field into the value attribute of the Form field to pre populate it.
An example of the user field code it.
[types usermeta='field_name' current_user='true'][/types]
Just replace field_name with the actual slug of your custom field.
