Hi. This is outside the joomla, template and SP PB. You need to prepare an image before uploading. If you need a certain static size, but not responsive, open the source code of your svg images in any HTML editor and add to the <svg> tag the width and height attributes that you need.
Exemple
<svg some-other-attributes-not-delete-them width="50" height="50">
....
</svg>
If the width and height attributes already exist, simply change their values.
Another way - you can set the size through your own CSS code.
Add your class to the addon css class field and use following code with value that you need
.your-custom-addon-class img {
height: 50px;
}