Did you buy a Subscription on Steam or directly from Adobe/Substance?

If from Adobe, I don't know if you can do a back link from your Substance account to Steam to get the unlocked product.
Similar to buying a game from an outside commercial source that is also available on Steam, you can't get the Steam version without re-buying it on Steam. There's nowhere on Steam to enter the activation code for the bought product that I know of.

But that said, I have the Steam version of the Substance products here. When I log into my Substance account through https://substance3d.com/ there used to be a link available to link my Steam account (I think the link used to be called Partners and there was a link to link accounts). I don't see that link page on the new Substance site. It may be something that has to be done when setting up a Substance account now (I don't know).

However when I go into My Licenses, I see my current products and the links to download previous versions for them (in accordance to my paid subscriptions).