It focuses on increasing the percentage of traffic to take a desired action, such as making a purchase, signing up for a newsletter, or downloading an article.
CRO helps your business by optimising how much of your traffic takes the desired action once they are present on your website.
I presume your home page isn't optimised for closing people. It showcases your business and links to other pages.
No it's the process of A/B testing call to actions, seeing data and insights on how long people spend on pages, modifying images and creating content that will retain more attention.
You have an issue with conversion. You could get all the traffic in the world and if your site is not optimised for closing, people wont buy. You can easily buy traffic via ads. Traffic is never the problem its converting that traffic to paying customers.
It doesn't directly impact your SEO but it can certainly help with it. If your site is optimised. More people will stay on it, therefore search engines think its a more relevant site and push it higher up it's list.