jj makes this extremely easy by the way. One sample way to do it:
1. jj new (create new change)
2. <make typo fix>
3. jj edit @- (please go back to editing the previous change: @ is the working directory, - means previous. kinda like HEAD^ in git)
You're done in a few seconds, and can get back to your regular work, while that change is split out into its own thing. If you're not as comfortable with the anonymous stuff, you could also `jj new -m 'typo fix'` to set a message then, but for small stuff like this, I don't personally bother until I am done with what I'm actually working on and am ready to submit that too.
If you’re treating @ like the git index (sometimes called the “squash workflow”) then you’d just do the same thing you do in git: squash each part of @ into the proper commit.
Of course, you could also just make it in the current change, and split it out later, but that's easier to forget imho.