Well, - I would have tried to helped you if you had posted some details on which connection you want to cut...
The profile have to be public or you have to invite the curator temporary into your family group to give access if you want the help on a private profile.
The "Removing these connections will split the tree." is a warning you get if the action results in profile(s) without any connection to a tree. We call them floaters or driftwood and is a situation we try to avoid, hence the suggestion on doing some more research on that line/profile to find if there are connections (spouses, siblings children, parents) that can connect them again.
If you find such a connection you will also be able to remove the bad connection without getting the error message.
