If you have an asset that is wider/higher than your slide, you can set a new position for it.
Click on the main asset lane
Open "Main asset behavior" in the side menu
Change the X- and/or Y-position of the asset
X-position
Y-position
If an asset has the same format as the storyboard (for instance a square asset on a 1:1 storyboard), this control won't make any difference.
Exact positioning of the asset
Custom Horizontal Position: Toggle on for more granular horizontal positing of the main asset, overrides the preset options on X-position.
Custom Vertical Position: Toggle on for more granular Vertical positing of the main asset, overrides the preset options on Y-position.