The first and simplest/least negative is to get Hitler to designate a successor before he dies, and (if you want to tank the hit) announcing it (which makes it even more effective). This costs a decent chunk of time and PP but it helps in the long run if you want to run a Nazi-loyal path. In order to do it you basically need to support a given candidate enough times in things like the decisions, and then you will eventually activate the modifier that Hitler has shown favor to them and can designate them as successor through the decision panel.

Keep in mind you can have the choice of multiple successors in a given time and can pick.

Secondly is mostly if Hitler dies without choosing a successor, in which the Reich's various government officials start butting heads with each other over power and whatnot. This means you're going to have to take risks or make some damaging compromises, depending on how badly you want to avoid the Civil War, how much risk you are going to take, and so on. In particular the SS and Heer paths are extremely risky because they involve either making a compromise with the other or trying to disarm them with a very low chance of success.

But it can be done, and it is somewhat easier to pick the "Political/Party" Fuhrers bpeacefully like Goebbels, Speer, or Bormann.

you can also make goering win if you do his economic policy, allow him in the senate, bormann do what he want first (him not joining speer) and obey the senate at the second time. And the military voting for goering and not allow eva braun to speak.