You can export any work that has been imported from CONTENTdm via the export tab in the project owner dashboard for the collection.
Only (and all) the works that are 100% transcribed and have no pages marked "needs review" will be sent to CONTENTdm. We update the the field you've set up as full text search. You'll need to update your index afterwards.
The next time you export to CONTENTdm, all of the 100% transcribed works will be sent, including the ones from the previous export.
It's not currently possible to export individual works to CONTENTdm.
You can see an example of an exported transcript in CONTENTdm on this letter from the Sandy Spring Museum. (Click on "transcript" immediately under the page image.)
For more details on the CONTENTdm integration, see Crowdsourcing with CONTENTdm and FromThePage.