3 answers
The primary contact field should be a lookup field on the Account/Organization looking to the contact. To fill this in, simply click the search icon next to the field, and find the contact you want to designate as the primary.
If it is saying there are no matches found, try typing in some of the contacts name, or if you have, try clearing it and seeing what shows up. By default, without and search parameters, the lookup will show the last few records of that type you viewed. If you type in the name, it will actually search for it.
