I hope you're doing well.
Here's how you edit the title of a thread you've posted, including WSO threads:
First of, click on the "Edit" button located under your thread.
Then, click on "Go advanced"
After that, you may now edit the Title and/or the body of your WSO if need be.
You may put a reason on top of it, too.
Then just click on "Save Changes" and you're done.