At the end of a song, this game will always show you your total average offset under the Timing tab, so if you know you stepped accurately to the beat, you can subtract this value divided by 1000 from the current global offset to get a more accurate one.
From my experience this is actually much more exact than even the Stepmania 5 auto sync machine function, because this way you are taking the average over the entire song instead of it continually updating every few seconds as you play.
For example, if...
Current global offset = 0.000 (default)
Song average offset = 50 ms
go into options, and change your offset to be "-0.050" (make sure to include the minus sign)
Current Global Offset = -0.073
Song average offset = -8 ms
Change Global Offset to: -0.065 (negative number subtracting negative number)
^ Of course, keep in mind this is all assuming you stepped perfectly accurately on average, when in practice it's likely you may be a few milliseconds early or late overall. I personally tend to be a few MS late because I'm new to reading 9-panel and this still delays some of my motions slightly even on easy songs.
You can always adjust this later though. Just... anytime it feels like you're not getting Perfects or Greats when you think you should... you can check this offset after a song and maybe tweak by half of that or something to get a more happy medium where you can get the most Perfects.
There's also a lot of other stats you can check under the Timing tab, including even how many Miss/Good/etc you got on a *per panel* basis. They may at some point add a machine autosync mechanism, but there's already a ridiculous amount of data shown in-game to help you step more accurately, once you learn how to use it!