In any group where you have multiple memberships, click on your email address, located in the top bar of the page. From there, you can switch the Yahoo! Profile you use in the group.

If you joined the same Yahoo! Group with multiple email addresses, and if you've associated those email addresses with a Yahoo! Profile, then you can use this feature.

This way, you don't have to go to the My Groups page and re-access the group through the other profile.