Removing albums from a merged set does not seem to work

Select merged set -> edit -> fix track grouping (all albums selected) -> DOES NOT REMOVE THE MERGE!!

did you highlight the tracks you want to unmerge and select Remove.

No, but I do not want to remove the track, only correct the old typo.

Correction - that above reply of mine was not on topic, apologies for any confusion.

I accidentally merged albums inappropriately and understood the undoing of the merge was from “fix track grouplng” but that does not work so advice please on what I should be doing.