How to mark a modern page as a news article page?

When using the news web part in SharePoint Online, it displays content automatically from pages that are marked as news content. For example, if you select 'New Post' on the news web part, it lets you create a page that is a news page.

I've noticed that when you publish a new page for the first time, you get the options below. One of these options is to 'post as news on this site', another handy way of creating a 'news page'.

Now let's say someone creates a page on the site, but doesn't do it by selecting 'New Post' on the news web part. Instead, they've simply created a basic page, published it, but also forgotten to click the 'post as news on this site' button.

Is there a way you can take a standard page in your site contents and convert it (or mark it) as a news post? I can't find any obvious way of doing this, and the options from the screenshot above disappear completely after the first time you publish the page.