Import Workitems using csv updated the resolution date of all workitems

One of the project manager exported the workitems to a csv file, modified an attribute value of all workitems and imported the csv file with latest changes. After import as the Status and modified date existing in csv file the workitems status for resolved date changed to the current date of import. The reports displaying huge count of workitems resolved on import date, so is there a way to revert these changes and fix the issue.

Thanks,

Vinay