Cleaning Cases in Power Query

You could do it a few different ways. Here are 2.

1. See this article on writing a custom function in Power Query to emulate the SWITCH() function that DAX has. For a few changes. this would be fine. For dozens or hundreds, this would be a pain.
2. Create a correction table, then merge it with your original table. If a corrected gender exists, use it, otherwise use the source gender. See my file attached. You should be able to see how I added the correction table then did the merge. This would be best for a lot of changes.