Joan:
This should be fairly simple, especially if you access the question you had asked and the answer there.
Merely click on the green link with that person's name which will take you to their G2G Profile. From there you can click the link to their WikiTree Profile. On that page, you will see the link for sending them a Private Message.
On WikiTree.com and G2G pages: if it's green and underlined you can click it.
I hope this helps.
~ Keith
