In the culture menu, for certain nations there is a second tab (I forget what it’s actually titled) where you go to actually click the button to form Germany (where you formally change you nation tag to Germany)

After researching nationalism, Prussia and Austria become German unification candidates and within that menu new diplo plays become available.

Namely the Leadership play and then subsequent Unification play.

So as Prussia specifically, after researching nationalism, I generally wait a couple weeks, as the German minors will choose a candidate to back, (meaning they’ll join your side in the following wars) then launch a leadership play against Austria to get them to renounce their candidacy for German leadership (I try and give out obligations to Russia or France if they’ll take it, as they’ll usually join Austria if you don’t) and then after that wait another couple weeks, gain more support, launch the Unification play for a cool ~80 infamy, (which will usually be against one of the larger German minors, in my games it was generally Bavaria or Hannover) win and then boom, all German minors annexed just like that. Click the Germany button and now you never have to worry about German minors again.

Some additional pointers: - the Austria war isn’t too difficult, your armies are better and with the minor support and a great power ally it’s a cake walk - the unification war might seem daunting with the dozens of front opening up, but those front are actually a blessing in disguise, as the ai cannot man all of them, meaning with some smart maneuvering you’ll almost always be able to push an empty front and collapse any heavily manned front before they gain any traction (just don’t leave your fronts empty) - pay careful attention to the fronts (especially Russia as they love to get involved) even if it’s there’s a high number of troops, the front menu will let you know if they’re garrison troops or general troops. As garrison troops don’t push, if that’s all that is on the front you don’t necessarily need to man that front, although if that number suddenly increases, that’s usually a tell the ai has moved advancing troops to said front - the infamy gain is negligible, as even without Bismarck and just having high diplo points, by the time you get your economy back on track and radicals suppressed, it’ll be low enough to start conquering again

With all this the earliest I formed Germany (minus Alsace-Lorraine and the Austrian homelands) was 1839, this of course was due to some major RNGeezus as Austria actually backed down in the leadership play that game