Sometimes a Signage Player can lock up and freeze, the easiest thing to do is to restart the device, if you still have issues - connect a mouse, navigate to settings>apps>signage> clear cache. Still having problems, go to settings>apps>signage> uninstall. 
Download this link https://commbox.com.au/content/downloads/support/anapps/CommBox-Signage.apk onto a USB, Connect it to the signage player install it and add to your screens list at signage.commbox.com.au