I am completely clueless about this, and hopefully Susan is right and it would be automatic, but ...

Regulation §1.1502-75(c) is where it mentioned that election, and you must have "good cause" un-consolidate them.

https://www.law.cornell.edu/cfr/text/26/1.1502-75

It says you need permission, and based on this PLR, it seems like you might need to do a PLR, which is challenging and expensive.

https://www.irs.gov/pub/irs-wd/0944014.pdf