How to add validation on the click of Submit Button in Purchase Requistion Screen in RSSP Page

Summary:

How to add validation on the click of Submit Button in Purchase Requisition Screen in Redwood Self Service Procurement Page.

Content (please ensure you mask any confidential information):

We have a requirement to validate if the Address is Provided in DFF(Additional Information) section then the "Delivery to Location" should be defaulted to a Specific Value. There is no option to default the Delivery to Location code using VBS . So we have to place a validation on the click of the "Submit" Button to check if the User has placed the required Delivery to Location code on Submission to capture this check. Please let me know if there any option to add this validation