1) google for relevant sites using the operators mentioned by
@The SEO here:
https://www.blackhatworld.com/seo/unlimited-niche-guest-posting-and-niche-edit-opportunities-in-just-1-hour-a-day.1588897/
2) check out these 2 lists uploaded by
@Steptoe:
https://www.blackhatworld.com/seo/5000-wordpress-sites-accepting-guest-posts.1539507/
https://www.blackhatworld.com/seo/1000-sites-accepting-guest-posts.1637864/
3) buy the yearly subscription to http://RocketGuestPosting.com to find, and outreach to relevant sites in your niche.
4) check these 2 sites out for guest posting opportunities:
https://bloggerspassion.com/guest-posting-sites-list/
https://solvid.co.uk/180-websites-that-accept-guest-posts/
5) check out various link building networks / SEO agencies like...
https://adsy.com/
https://www.guestposts.com/
6) pay content syndication networks like https://www.thehoth.com/content-syndication/ to send your content out to various sites (blogs, media outlets, etc)
Disclaimer: I'm not affiliated with any of these sites, so I can't vouch for any of them. I've just linked you with these resources but whether or not they're what you want in terms of price, relevancy, professionalism, etc is up to you and them, so do your research on them yourself before jumping in, head-first