The EE critical pages are all dynamically generated so you can’t edit them as ‘page’ within WordPress, at least not to make the changes you are looking for.
The text for that specific section is filtered via PHP and you can use a custom function to return whatever else you prefer, for example:
The simplest method to remove details from that output is to hide it using CSS. If you can take a screenshot and highlight the sections you want to remove I can give you some examples.
CSS is for visual changes rather than changing the source code of the site (such as text changes) so you can hide the elements you want to with CSS but not the congratulations text change.
This CSS should so what you have requested in the images:
The support post ‘How do I edit this thank you page’ is closed to new replies.
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Support forum for Event Espresso 3 and Event Espresso 4.