How would I make an animated mob (with blockbench)?

So I've been working on a custom mob, and I animated it accordingly. The problem is that when I go to the latest version and try to export it, there is no animated java option, which makes sense. Then when I go to version 3.6.6, the required option, I can't export it to the needed version, the latest being 1.15. Does anyone know how I would go about this?

(sorry if this is asked weirdly, this is my first forum post.)