1. Log into Dynamics with an account that has admin rights
2. There's probably a couple different ways to make this happen. But I'll show you what I did to make this work. Click on Cards, Purchasing, Buyers
3. With the buyers window open, click on the Look up icon (Ctrl+L) and find the user you need to set up (In the below example I'm using Debbie Clark). Type in a description and then click on the Look up icon under the User ID section and find the user ID that you would like to link to. Click Insert and then click OK.
4. That should do it. Oh... if the user is currently logged into GP. Have them exit GP and then log back in for the new setting to take effect.