My guess is they simply bobbed the hammer.
Pull the trigger a little to get the hammer moving and then use your other hand to set the hammer taking your finger off the trigger.
If the hammer sets. Then it is simply a bobbed hammer.
If it does not set it is a DAO and as Dee said, replaceing the the hammer and the trigger will simply be replaced.
and ta da. DA/ SA revolver.
Other than that just use it as a DAO till you get the parts.