Hi,
First of all you need to find the wrong record with combination of that wrong date.
From error message you will know date info object, from that date info object you can find which source field was mapped(transformations). thru that you will know source field.
now delete request from dso, Go to PSA--->manage--> select wrong records,
once you open psa data, keep filter date field(which was mapped dso date info object), enter the value which was wrong and display it.
it will open the record which was wrong one. click on it, select edit and change correct date and save. retrigger your dtp and activate it later.
Thanks