Well, there's no 100% warranty software which can restore previously formatted data. If you have a copy of data (OS system), you can try to restore them from that backup. If not, you can only restore Windows OS (clean installation). Dell provides a way to achieve that. Note: you'll need
Dell Servive Tag
(on the bottom of laptop). See:
Dell Windows Backup Media and Recovery Options | Dell US[
^]
BTW: i'd strongly recommend to change repair technicians and/or workshop...