Thank you for using the Trusted theme.
This can be done with custom CSS (Customize > Additional CSS):
/* remove icon of 1st featured service */
.featured-post1 .featured-icon .fa:before {
content: "";
}
/* replace icon with own image */
.featured-post1 .featured-icon .fa {
background: url('image-url');
width: 40px;
height: 40px;
background-size: cover;
}Or you could upgrade to Trusted Pro which has the option to quickly and easily add your own images in place of the icons in the customizer.