If you have unused tickets in concur, can you just book the flight and then the site automatically accepts the credit before charging you? I dont see a way to actually select the unused ticket to use.
I always advise my employees to call the TMC if there is a ticket to apply. It should flag and queue the reservation to the agency to have the credit applied. However, it is easy for the credit to be overlooked.
Much easier to make a quick call or send an email to make sure the credit is applied correctly.