One of the easier way to optimize your wordPress sites Robots.txt File, is if your are using Yoast SEO plugin. The plugin comes with a tool section that gives you access to create and edit your Robot.txt file. To do this, simply go to Yoast SEO plugin,>> Tool>>File editor, click on it and a new page will open and you will see the default WordPress robots.txt file there.

To optimize, simply copy and paste the code as it is below to the box that says Robot.Txt. After doing that, change the www.yourwebsite.com URL to yours.

User-agent: *
Disallow: /wp-admin/
Disallow: /wp-content/plugins/
Disallow: /readme.html
Disallow: /trackback/
Disallow: /wp-includes/
Disallow: /go/
Disallow: /xmlrpc.php
Disallow: /index.php
Allow: /wp-admin/admin-ajax.php
Allow: /wp-content/uploads/ Sitemap: https://www.yourwebsite.com/post-sitemap.xml
Sitemap: https://www.yourwebsite.com/page-sitemap.xml

Source: https://www.gizmolad.com/2018/05/how-to-optimize-your-wordpress-robots-txt-file/