Go to your dashboard: http://www.conventionofstates.com/dashboard. At the top right, click on your name and choose "Control Panel" on the drop-down list. On the right side of the menu bar, hover over your picture then choose "Your Account" from the drop-down list.
On the right side of the screen, move your personal email down to "Email 2" (or 3). Then enter your cosaction.com email address (e.g. joe.lastname@cosaction.com) in the "Email 1" field. [Or whatever address you prefer to be primary.]
(You may have to log out of all COS-related sites and log back in before this change takes place.)