Multiple domains on one site

Hi all, I seem to be drawing a blank here. I have done this before but cannot seem to find the proper walkthrough on how to add a second domain I already own through Squarespace to one of my Squarespace sites. Here are the details - I have a .ca domain which is already my primary domain for a live website , I have another domain .org that I want to forward to the primary .ca domain.  Why can’t I find the simple instructions on how to do this? Maybe I’m tired. lol.  Note: both domains are in my domains dashboard and are purchased through Squarespace. 
thanks

You don't forward one domain to the other, the primary one always appears in the browser bar regardless of which domain was used to load your site.  I have two Squarespace custom domains this is my primary one:

derricksrandomviews.com

This is the "secondary" which was my primary for years.

myrandomviews.com

If both of yours are in your website settings you choose the three dots next to the domain click that  a panel comes up with set as primary domain. 

Sorry let me clarify. They were purchased separately not tied to one website. So they appear in my domains dashboard but when you go into website / domains and email only the primary is listed. The 2nd domain only appears in the domains dashboard.  Hope that helps explain my issue. Thanks

18 minutes ago, paul2009 said:

@Seylerg To connect the second domain to your site: 

1. Open your Domains Dashboard.
2. Click the domain you want to connect.
3. Along the left side, click Website.
4. Click Connect existing website.
5. Select the new site you'd like to connect.
6. Click Next, then click Confirm.

Did this help? Please give feedback by clicking an icon below  ⬇️

Perfect thanks.