With Routine, you can connect as many accounts as you want so as to manage all your calendars & contacts through a single workspace.
First, head to Settings, then Accounts to manage your accounts.
Click on + Add Account
to connect an additional account. Your default browser will open requesting access to your calendar and contacts.
Once the permissions granted, the new account will appear in the list of connected accounts.
The calendars attached to this new account should also appear in Settings/Calendars.
You can now pick a color, enable/disable the calendar but also define if the calendar is primary or secondary. For more information, please refer to .Set primary calendars