So pick the lowest WikiTree number for the 3 profiles, and that's going to be your target for the merge. When you finish, this will be the remaining number.
Initiate a merge, you'll have a top box and a lower box. The higher numbered profile goes in the top box, the lower number in the bottom. Click the button to kick off the merge then provide the reasons and submit. Because there are 3 profiles, you'll have to do this twice. So if you were merging (for example):
Brown-1, Brown-2, and Brown-3
Brown-2 gets merged into Brown-1
Brown-3 gets merged into Brown-1
Only Brown-1 remains when all is done.