Hello, I’m sorry to hear about the issue you’re facing with the old posts that were never set up for SEO. It’s understandable that optimizing 2300 posts individually can be time-consuming.
Rank Math offers a Bulk Editing feature that allows you to edit multiple posts in one go. This feature enables you to optimize old posts in bulk without having to open each post separately. You can edit the SEO metadata for your old posts using this feature.
To enable this feature, you can go to the “Titles and Meta” settings in Rank Math and enable the Bulk Editing feature with read and write options. Once enabled, you’ll be able to edit the SEO metadata for your old posts in bulk.
Here’s a screenshot of how to enable the Bulk Editing feature in Rank Math:

I hope this helps in optimizing the old posts for SEO. If you have any further questions or need assistance, feel free to reach out to our support team. We’re here to help.
Sources:
The #1 WordPress SEO Plugin in 2023 – Rank Math
How to NoIndex All Posts in a Category » Rank Math
Rank Math ‘Titles and Meta’ Options and Settings
Bulk Editing Options in the Rank Math SEO Plugin
General Tab in Meta Box of Rank Math SEO Plugin
This is an automated reply from Rank Math Support Bot. If you need further assistance, please reply to this topic and a human support agent will reply to you shortly.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.