Tracking down old pension? Any advice?

Just received a notice from SSA that I may be eligible for a pension from a firm I worked at years ago. It’s not an insignificant amount. That company, though, was bought by another company, that was then bought by another, etc.

Anyone have experience trying to track down retirement benefits like this? I’ve already done a bunch of internet searching to no avail. Are there attorneys or services that I could hire? How does this work?

UPDATE: thanks everyone for excellent input! So, I spent another block of several hours researching, emailing, calling - and finally tracked down which company is responsible for the old pensions. They directed me to call a special number at Fidelity.

Fidelity did some research and found out …. Drumroll Please …. That the “pension” was actually an old 401k. I had rolled that money over many years ago into what is now my current portfolio.

Oh well, it was fun to dream - for a moment - that my ship had come in haha. Onward!!!