There are ways of increasing engagement and ranking with guest posts, even after the blog post is published. One of these is sharing consistently on social networks.
There is no harm in promoting your guest post, given it is a win-win for both you as a guest and the blog host.
You can share your content on Linkedin, Twitter, Facebook, Instagram, Pinterest, and any other platform where your audience might be. The larger your reach on social networks, the higher the engagement and the chances of getting picked up by search engines.
Promoting your guest post ensures that content ranks better on Google, consequently generating more traffic to your website.
You can seek the services of social influencers for promoting your content. While this is not free, the rewards of influencer promotion are always worthwhile.