Start by finding MD3 Maintenance in your Windows start menu:
Select the 'MedicalDirector Clinical' under the Database Tasks and then click on the 'Diagnosis Coder' icon:
This tool will show you all uncoded past history entries on the left side of the screen. You can then select the uncoded item on the left, find the correct, coded diagnosis on the right and by clicking 'Link or Correct' all instances of the uncoded history item will be replaced by the coded one:
If you prefer to continue using the free text item you can just click on 'Link' and all current and future entries will be linked to the correctly coded term.