Question

If you already have a reasearch question identified what should you do to create a thesis statement

Answer 1

A thesis statement is simply the writer's opinion about the topic (and possibly the inclusion of your supporting points to be explained in the following paragraphs.) In this case, it would be your "answer" to the research question.
A VERY, VERY SIMPLE example:
Should marijuana be legalized?
Marijuana should be legalized (because......)