Making URL redirect from an ACTIVE page in main navigation

Site URL: https://alliance4water.org

I manage two "sister" websites run by the same organization with slightly overlapping audiences. I would like to make a more obvious link in the main navigation to my second website, which has a different domain. My plan was to create a new blank page for the main navigation and do a simple URL redirect to the other domain, but Squarespace overrides the redirect and sends people to the blank page because it's "a reserved URL slug."

Is there any way to get around this?

Thanks in advance!

I'm relatively new to Squarespace and didn't know that was an option. THANK YOU for the tip! I have only made "basic" pages before (blank, blog, events, etc.) and didn't realize I could simply add a link like that. I was making it harder than it needed to be. Appreciate the basic tip, tuanphan!