Contact an employment attorney. They'll take the case on contingency if they think it has merit. Small employment claims are common and employment attorneys are very familiar with the intricacies of U.S. employment law (of which the ADA is a huge part).

They will almost always give you a free consultation about whether you have a claim, if nothing else.

I would not look into legal-self-help kinds of stuff until you contact a few employment attorneys and none will take your case.