The tutorial I read is based on 2.79. So I'm not sure if it's still the same name in 2.8. But I can't find anything providing similar functionalities.
It can be found in the 3d Viewport:
As well as in the Edit menu where it is called Adjust Last Operation now, where you can also right click it and choose Assign Shortcut if you wanted to be able to call it with a keyboard shortcut like it was with F6 in previous versions:
Obviously, it does not need to be F6 and could be anything that is convenient to you.
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$\begingroup$ This is very similar to How to reduce poly number when you start creating object in 2.8? , however I think the question is formed a lot clearer so I think it makes sense to have a clear question and answer here to be able to link all the possible duplicate variations of it in the future. $\endgroup$ – Martynas Žiemys Jan 17 at 10:26