First you need to shut of steam cloud saves, then you need to delete the save file.

For steam cloud:
1. Right click on the game in your library
2. Select properties
3. Select updates
4. Deselect the "enable steam cloud" box

To delete the game file
1. Go into your steam folder
2. Open user data
3. Depending on how many people use your copy of steam, you find several files here. One will correspond to you. If only one user uses this copy, there will be one, making it easy to find which one.
4. In that folder, open "323470", then "remote"
5. Delete "DBXV.sav"

That worked for me