What I did to find this plugin was to simply Google search for “delete wp transients” (without the quotation marks, of course) but for you, I will gladly share the one I learned was THE best plugin at this date in time, for deleting ONLY the outdated transients.

Delete Expired Transients by WebAware

Once you have installed and activated this plugin, look down the left-hand sidebar of your WordPress Dashboard... this time, under Tools, you will see “Delete Transients”... click on Delete Transients.

You should notice that the option to delete only expired transients has been selected by default. I highly recommend that you ONLY delete the expired transients.

Notice that my WordPress database for this website has 42 transients...
but I am only going to be deleting 33 of them. I have now clicked on the
Delete button.

Now I only have 9 transients remaining and zero expired transients.

You can now Deactivate and Delete this plugin before moving on.

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