I did it a little differently.
I obviously installed the extension.
Unfortunately, it didn't work for me either, so I wrote a little CSS code that works if someone wants to use it.
The code. Just paste the admin-CSS
.Badge.Badge--group--7.text-contrast--dark {
background-image: url('https://www.teteos.net/hasanmerkit/verified-blue.svg');
background-size: 22px;
border: 0px solid transparent;
box-shadow: none;
background-position: center center;
background-repeat: no-repeat;
}
I hope it works for everyone who wants to use it.