How to change a logo on a wordpress site that is part of a 7 site multisite?

Use CSS Trick to change the logo

Go to Site3 (site you want to change the logo) dashboard / Customize / Additional CSS place below code and and put your logo under wp-content/themes/bridge/img/

Here I installed bridge on local host and created 2 sites on network .

.q_logo a img{
background-image: url(wp-content/themes/bridge/img/pin.png)!important;
background-repeat:no-repeat;
height:70px !important;
width:90px !important;
object-position: -99999px 99999px;
}

I used pin.png image to display instead of logo, give width and height as per your logo size.

hope this trick can solve your problem