Did you create the ad yourself? If so you should be able to edit all aspects of the ad on the edit page. If you did not create the ad, you cannot edit any details.

Could you clarify what you mean by “ad” . . .

Is this short for adverting – you have an advertising campaign you want to edit?

Or are you using the word like eBayers – “ad” meaning the item you have for sale, and your description of it?

I believe now that I am probably on the wrong forum. My advertisement was not placed through Seller Central but through Amazon Advertising, via Amazon KDP. I see that it’s a completely different user dashboard. Never mind. I’ll ask Amazon KDP directly.

Advertising -> Campaign Manager ? You should be able to.

I have just had a reply from customer Amazon support (my highlighting):

"Hello,

I’m sorry for any disappointment this issue has caused.

You cannot edit custom text for an ad campaign when it is running.

You can change the cost-per-click bid and schedule of a live campaign. You can also increase (but not decrease) the lifetime budget. The campaign name, interest targeting and custom text of a campaign cannot be modified once the campaign is submitted.

You need to create a new ad campaign to change the custom text.

Although at this time there is no option for this, we’ll be sure to consider your feedback as we plan for further improvements.

Rest assured that I have passed along your comments to our developers. We definitely value your opinion and will continue to listen and respond to our publishers’ concerns. We will make every effort to evaluate the information you have provided, and try our level best to lead it to program changes or enhancements.

Thanks for your understanding!"

Given that this answers my question, I am no longer following this topic. Thank you.