Assuming the comment tagfield always contains a valid date string of format mm/dd/yyyy, then you may use the following actionsgroup to isolate and reformat the date string (tagfield DATE is saved as YEAR).
Begin Actionsgroup TEST
Action #1 Actiontype 5: Format tag field Field: DATE Formatstring: %comment%
Action #2 Actiontype 4: Replace with regular expression Field: DATE Regular expression: ^.+?(\d{2})/(\d{2})/(\d{4}).+?$ Replace matches with: $3/$1/$2