The Wrong Membership Level page can be set in the Advanced Options > Global Defaults > Error Pages section of WishList Member.
Logged in Members can click to access protected content and if they don’t belong to the Level(s) set to access that protected content, they are sent to the Wrong Membership Level page.
You can use a Page and include any additional info you want. There is also the option to simply use a Message or a URL. The available Tool Tip (blue question mark icon) beside each option provides more details if you mouse over them in WishList Member.