Juxtaposition Image Size on embedded code

Hello, 

I'm a french user, so I hope my translation will be good.

I've made an image juxtaposition on H5P.org.

I want now to import it in a presentation ( with genially) as an embedded element.

I've copied and pasted the iframe's code. But the image is too big for my presentation.

When I try to resize directly in my presentation by clicking on my inserted element, the view is uncomplete.

When I try to change the iframe's code, ( width and height ) the result is the same.

How can I do to resize the whole element ?

I need your help.

Thanks.

Laurent.