I do not know of a way to merge two reports into a single report. One solution and I have no confidence that it will meet your needs is to make one report a subreport of the other.
I really think you will are looking opening the two reports and deciding which one has the fewest items to move, then creating the single report in the designer.
I wish I had a better solution, perhaps others may have a better way to deal with the problem.
Regards,
John W.