@lara_e
If the iframe is embedded, you should check if there are any styles on the embedded iframe and change the "height" and "min-height" to something like 355px or whatever you think is appropriate.
Depending on how it's embedded these CSS styles may help, or not ¯\_(ツ)_/¯
iframe#iFrameResizer0 {
height: 355px !important;
min-height: 355px !important;
}
#iFrameResizer0.review-heading {
font-size: 20px;
color: #000 !important;
}