WP beginner may be able to help you

https://www.wpbeginner.com/plugins/how-to-convert-post-types/

I'm using the Post type Switcher plugin on my website to convert posts in pages or pages to posts. It's quick and easy to use.

There is a plugin called post type switcher install that and you can then change a post to a page or a page to a post. Wishing you well.

if you want to do it on your site - then there is a plugin for that
easy post switcher plugin will change a post to a page and a page to a post.
or copy and paste the contents to a post and trash the page.
the plugin is the easy one if you have the content indexed.
good luck
phil

edit: as andre says the plugin is called post type switcher not as i said above easy post switcher, so appologies for any confusion

Anyone can correct me if I'm wrong but I don't believe you can. What I've been doing is:

1) Save the page as a template.

2) Open the template in your content area.

3) Publish it as a post then delete the previous page.

If there is an easier way to do this I would sure like to know as well.

Kind regards,
Brandon Sandy