Saves include all unlockable items from all game events, except for those that are unlocked in the DLC. You can open them with DLC Unlocker
There will be two kinds of saves in the folder;
0% progress, for those who want to start over and don't care about unlocking weapons or items
100% progress, for those who just want to play with friends or online.
Installation: Steam\steamapps\common\Deep Rock Galactic\FSD\Saved\SaveGames
Rename the downloaded Player.sav file by adding your steam id to the title
In the SaveGames folder you will see how the save should look like, for example 76561198201254354_Player.sav
Don't leave the old save file and the new one in the same folder!