How do I remove my iCloud from the Apple Watch I sold?

I recently sold my apple watch. Problem is I went to iclou.com to erase it and i did a mistake in my password which made it dissapear on the icloud.com. So i erased it from my iphone settings in the icloud part and now the buyer tells me that my icloud is still on i really dont understand and know what to do

[Re-Titled By Moderator]