Do you have a back-up disc made before the mistaken merge? If so, you could load that and then save it on computer to eradicate the error, but you would also lose recent entries.

I have found to my cost that it is good insurance to have a back-up disc when there is loads of data on a program, then, if the computer crashes, as mine did twice last year, all is not lost............

Hope you find a solution,

Janet.