There are 3 ways for you to add a logo to your video.

First, click the Overlay button, and you will find many Logo overlays. Select a suitable sample and click to add it to the canvas. Then back to the media part, drag the image you like to the logo frame.

Second, click the Replace button and select an image to replace the original logo. 

Third, click to add a PiP to the storyboard.  

You can change the shape of the logo as well (remember to ungroup first if the logo sample you added has texts).