To add a second Wealthsimple account, you will need to logout from the previously connected account on Wealthsimple side. You can do so by going here https://my.wealthsimple.com and logging out. This applies to both Wealthsimple Trade and Wealthsimple. If a session is open already on the portal, this account will get added to the dashboard.
Please open an incognito window to add the first connector, then close the browser entirely, open a new incognito window, and add the second connector.