Each selection item should be on its own line. The selection is broken into two parts: the value and the label. The value is what is submitted back to the server. The label is a user-friendly description of the value. A pipe-symbol separates the label and the value Example: You might want the selection's label to say "Contact our customer support" and all you need as the value is to say, "Customer support".
Each line would read: "Customer Support | Contact our customer support"
Screen grab of an example:
Note: The line with "|Please select one" means the selection has a value of nothing (or null) even though the label reads "Please select one." By setting the field to be "required", this selection will not be accepted until the user picks an acceptable other choice.
Instructions from RS Forms can be found here:
https://www.rsjoomla.com/support/view-article/827-dropdown.html
The complete form field knowledge base can be found here:
https://www.rsjoomla.com/support/documentation/view-knowledgebase/180-form-fields.html