There is no built in zoom in the whiteboard, but you can accomplish this in 2 ways.
Expand or shrink contents on the whiteboard
Use the select tool on the toolbar (it's the one farthest to the left)
Click and drag across the entirety of the contents you want to shrink or expand, including text, images, drawings, and anything else.
Click and drag the selection bumpers to shrink or grow the contents together. You can then move these around the whiteboard to put them where you would like.
Use your browser
If you simply want to see a closer or farther view of the content, you can also zoom out the UPchieve app and whiteboard using your browser's zoom function. For example, press Ctrl + - (Windows) or Cmd + - (Mac) to zoom out.