So I recently bought Icewind Dale, and I'm excited to play it for my party.  I wanted to print a poster of the world map for my players, but when I sent the file that comes with the book to Walgreens, they said they couldn't print it as it is copyright material.  They said I need a copyright release for permission and I search all over the book and dnd beyond forums, but haven't found anything that says where to get that.  I'm confused cause I bought the book and I'm just trying to print one poster for personal use so I would really like to figure out how to get this "copyright release."

It is allowed, but getting print shops to realize that can be a hassle

The Wizards of the Coast Fan Content Policy covers that.
Two key excerpts:

1. One word: F-R-E-E. You can use Wizards’ IP (except for the restrictions listed in #3) to make Fan Content that you share with the community for free. Free means FREE:
   • You can’t require payments, surveys, downloads, subscriptions, or email registration to access your Fan Content;
   • You can’t sell or license your Fan Content to any third parties for any type of compensation; and
   • Your Fan Content must be free for others (including Wizards) to view, access, share, and use without paying you anything, obtaining your approval, or giving you credit.

You can, however, subsidize your Fan Content by taking advantage of sponsorships, ad revenue, and donations—so long as it doesn’t interfere with the Community’s access to your Fan Content.

...

So, what exactly is Wizards IP?

Wizards IP includes the cards, creatures, books, games, gameplay, pictures, stories, logos, animations, artwork, plots, locations, histories, characters, graphics, files, text, and other materials published by Wizards of the Coast.

There is also this tweet from D&D Beyond

Otherwise you can contact Wizards Support

Thank you!  I will definitely be showing the stubborn lady at Walgreens these sources :)