HI, When you open the app select Books ( at the bottom of the app ) and at the top right hand corner is a box with a arrow tap that then settings, scroll down to reset scores, "WARNING" you will reset the app and remove all scores and start afresh, or ( I've not used it but had a look for you ) select the book your working on, you are now at the Actions for book screen scroll down and hit Reset timeout from the menu, its 4th from bottom.
I am still finding my way about the app but hope that helps.