how do you get into macbook that has flashing question mark with support.apple.com/mac/startup

Looks like you started another post for the same issue. As jeffreythefrog has indicated, and from the article you came here from, you should have the steps needed to try to resolve this. Please don't double-post.

If none of this is helping, then I would suggest that you contact Apple Support directly. To do so, simply select the "Get Support" link in the upper right-hand side of this forum's web page.

you can see if this apple support page helps: if your Mac starts up to a question mark