Google prioritizes fresh content. That’s why it is important to let the crawlers know about the updates done on your website. Your website will not be prioritized if the crawler is not able to learn about the changes.
Use Search Console
To let the crawler know about the change you can use the search console. Submit the sitemap.xml. There is an option of submitting the URL if you have made changes and it is not being noticed by the crawler.
URL inspection tool
The URL inspection tool can be found in the Search Console. It can be used to check how the URL is being seen by the crawler. You can use the same tool to index your new page if it has not been indexed by now.
If-modified-since is a header that let the crawler know about the changes made on the webpage. Even Google recommends this header support to your web hosting.
Make sure that your web server correctly supports theSource: Advanced Webmaster Guidelines By Google
If-Modified-SinceHTTP header. This feature directs your web server to tell Google if your content has changed since we last crawled your site. Supporting this feature saves you bandwidth and overhead.