You will need to edit the form. The field is in the works table. You need to add the field ExtendedDescrtiptionText to the form.  If you are unfamiliar with Crystal Reports then get with your reseller.  Normally I use a formula that says if the ExtendedDescription key is greater then 000000 then ExtendedDescriptionText else ItemDescription.  This way if the item has a description of less than 30 characters it prints.

There is a document on Sage's Knowledgebase to assist in addition to what BigLouie  has suggested.
https://us-kb.sage.com/portal/app/portlets/results/viewsolution.jsp?solutionid=223924350031841&page=1&position=3&q=how%20print%20extended%20description