Love my Unlocked S8+ but how can I find MultiLine

[AC Question]

Love my S8+ but can't figure out how to turn on MultiLine on my unlocked phone. All the carrier instructions show how to do it when loaded with their crapware but not a mention of it can I find on Samsung's site for the unlocked model. Anyone got any suggestions. I'm on T-Mobile and want to use the Digits service which requires it but don't want to use their apps. They say I should be able to use the native Samsung Apps with it if I can find how to enable it.