Phenomenal to me that you would have lifetime coverage for this particular type of condition, but since you're in CA. I guess it could be possible. In my area of the country, it's usually set up so that it's good for two years after the last occurrence of the condition. Twenty-one years ago is such a stretch!
But even so, if you were to need treatment for it again now, at this point, what you'd need--(and I would try to get this from the company first, go through their HR, instead of paying a law office to see if they have old copies of the information) I'd call Bank of America, starting with their HR department. A company this size likely will have a worker's comp department, and maybe HR can direct you to them. Then you try to figure out who was the worker's comp carrier at the time of your case (sometimes they change them, but should be able to tell you who it was back then) and then you'd also need, if they can provide it to you, your claim number. If they have any records of your case, they should have the claim number. Then you would need to contact their provider who processed your claim back when with the claim number, and tell them what's going on.
I'd do this myself, I wouldn't depend on Bank of America to contact the carrier for me. When you call the carrier, you'll have a better idea of what your settlement said exactly, and how to go about getting reimbursement for treatment now.