How can I hide certain elements inside of an iFrame?

I have put this iframe code inside an HTML RapidWeaver page:

<iframe src="https://www.hiorg-server.de/kurse_extern.php?ov=rhio" scrolling="auto" width="1280" height="2100"></iframe>

Now I would like to hide certain elements inside of that iFrame (see screenshot). Is that possible?!?

Here is the published page: https://www.asb-birkenfeld.de/2023/angebote/kurse-offsite/