Not sure if you still need help with this, but I just found a quick way that works fairly well. I used the alternative method of adding an HTML tag to my squarespace website. Follow this list of steps:
(if you already have the HTML meta tag - skip to step 5)
1) Open YouTube Studio site
2) Click on Settings tab on the left pane under your channels logo
3) Click on Channel tab, then click on Advanced Settings, then scroll down to click on Advanced Channel Settings
4) Scroll down to Associated Website section, then click on Alternative Methods to find specific HTML meta tag to copy.
5) Now open your Squarespace account to edit website settings
6) Click Settings tab on the left pane
7) Click Advanced tab
8) Click Code Injection tab
9) Paste your HTML meta tag into the Header section, then click save
10) Return to the YouTube Studio site, and click Verify
This seemed to be very simple compared to the first method. Hope this helps!