Do I even need to for my Hitman 2 data to carry over to Hitman 3? I bought the game through the Epic game store, but I linked my Epic account to my Steam account. I’m confused. 
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Be warned: progress carryover is a one-time thing.
Once you’ve done it, you won’t be able to transfer progress again, in any direction, as it stands as of right now.
IOI Account required for carrryover process. You can create it here: https://account.ioi.dk/
Transfer progress website is here: https://profile.hitman.com/
But this procedure might not work now as of the high load.
I suggest you wait till tomorrow maybe and then do your transfer.
When you created your IOI Account, log in to it with your Epic account, not by email or any other way, choose log in with Epic. And you should be done. It might not work for the first time, just try again