1. Find the mod forum post from the community: https://www.draftdaysports.com/board/viewtopic.php?f=254&t=27589
And/Or Download HistoricalPlayerData.json from here: https://drive.google.com/file/d/0B-Y8xLPX-AmWSWtUVVRrS25nME0/view?resourcekey=0-Xzmn5SWp_tMF_XJwVL-vDA
2. Place file in Documents\Wolverine Studios\DDSPF 20xx\ folder
3. Create New League and set the options below. Import year is the year you're pulling in from your historical file.
4. When creating your league select a league format that matches the era of the teams you're importing. You may need to download other "real world" style mods or create custom teams.xml files to match up with the team id's in the mod file. Otherwise players will get dropped into free agency or placed on the wrong team.
5. Select "Place on Team" to get the players to import onto their correct teams, or use one of the other methods as preferred.