There is no default module currently available on the HubSpot CMS for a pop-up modal so this is something that would best be built within a custom module.
By building a custom module you will be able to specify some JavaScript that will display/hide your pop-up on a certain click.
If coding is not your thing however you could always have a look through our Asset Marketplace to see if you can purchase a ready-built module that suits your needs. Here is one option that I found on a quick search!