Find the answer that is provided to you. On the bottom of the comment, there is an option in gold text that allows you to pick brainliest. You can try it on this comment.
After you thank them or rate them (I'm honestly not sure which, but why not do both if you're going to do one anyways), a yellow button will appear (I think next to the 5 stars) that says 'mark as Brainliest'. If you click that button, the answerer will get a notification saying that you marked them as Brainliest.
P.S.: Only the person who asked the question can mark an answer as Brainliest, and only one person can be marked as Brainliest.
