Hi,
you should look for a decent TESOL course offer in your local environment, I would advise against an online course for two main reasons:

1. They normally cannot offer the essential practicum environment, and practice is essential prior to really teaching a class.

2. Most of the online curricula are poor in content and do not cover everything needed like introduction to a different set of methodologies. They normally concentrate one one methodology only.

And with your previous background in education, you will probably know more and learn nothing new in such an online course.