What happens to MRA when you switch health insurance companies?

I might be switching from Cigna to Aetna next year because of network changes, but I can't seem to get a straight answer on where the MRA money goes if you switch companies.

I called Cigna and they said they send the money back to JPMC (makes sense since JPMC funds the MRA)

I called JPMC ASK HR and don't really trust the answer the rep gave. They said something vaguely along the lines of "we can move it over".

Has anyone done this before? I have a fair bit on money in the MRA and I'd hate to lose it.