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. It's important to log out between adding two different Wealthsimple accounts.
After that, you can come back to Wealthica and add another account in the +Add section