There isn’t an easy way to merge the content of the two fields. I’m not going to say that it wouldn’t be possible, and while I have some idea of all of the changes that would be required, I’m not sure that I could explain it all. You’d have to update all the meta_key values, all the meta_value values that point to the ACF field keys and all of the flexible fields to contain the serialized array of the new group.
I think it would probably take less time to copy and paste the data than it would take to build a tool to do the work.
