Chrome is blocking third party cookies; asking me to set Same Site attribute = None and Secure, but does not specify how or where?

Question

This is the message I am getting using a Leaflet.js heatmap, and I can't see my circle markers, and I believe this is most likely the issue.

Because a cookie’s SameSite attribute was not set or is invalid, it defaults to SameSite=Lax, which prevents the cookie from being sent in a cross-site request. This behavior protects user data from accidentally leaking to third parties and cross-site request forgery. Resolve this issue by updating the attributes of the cookie: Specify SameSite=None and Secure if the cookie should be sent in cross-site requests. This enables third-party use. Specify SameSite=Strict or SameSite=Lax if the cookie should not be sent in cross-site requests.

I am using Javascript, and the video from Chrome said to do:

Set-Cookie: cname=cvalue; SameSite = None; Secure

But where do I do this?