Total War: Warhammer III

This can be easily done in the course of the campaign. To invoke the Motherland, simply click on the palace looking button next to the deamon soul score and choose one of the four invocations. You can do that every ten turns, i.e. the earliest you can have this is by turn 40 or after your first deamon soul.

You will need devotion to be able to invoke it, too. You can get those either from the green building chain "Orthodoxy District", the "Grand Citadel" in Kislev, the "Bokha Palace" in Kislev or by the effect of the chosen invocation. All invocations can useful to quicken the acquisition of devotion, it depends on what you do.
If you know you are going to conquer a few settlements in the next couple of turns, choose "Ursun", if you will battle a lot "Tor" is the choice for you.