Thanks for using the Yoast SEO plugin. What you reported sounds like the meta box is missing under the default content editor. You should find it as referenced in this screenshot. If not, please provide us with screenshots that highlight the issue you are experiencing. You can use any image-sharing service like https://pasteboard.co/, https://snag.gy/, https://imgur.com/, https://snipboard.io/, or even upload the screenshot to your own website. Once you upload it to an image-sharing service, please share the link to the image here.