What are the skills and knowledge you could actually bring & fully realize at some point in the past?
And we're taking this in the strictest, nerdiest, materialist lense. I don't care how smart you are you ain't making a steam engine the in bronze age, for instance.
So what could you create, with just your knowledge & period tools? What kind of institutional, technological, philosophical innovations could you realistically recreate? How would you interface with the social fabric of society to not be some crazed pariah who never positively influences the place they went?
one key point is to tell them how the ships / settlements contain limited food, ammo, and other supplies, and that they can use siege tactics against them
And how the Europeans will use divide-and-conquer to take advantage of indigenous divisions and either annihilate or enslave them.