How would you cite a figure in MLA format if you are the author of it and the figure was not based off of any source?
If the figure were in another published work, you would cite it the same way you would if it were somebody else's work. Citing yourself is done when applicable; that's not an error.
You indicated in a comment, however, that you drew the figure for the purpose of the present work. In that case, you just include it as part of the work. Citations are for works that were previously available. You don't cite your own figures, tables, equations, or drawings if the current work is their first appearance. (You would then cite them in later works if the situation were to arise.)