Adding point on route extends route back from the end

I was trying to create a route from Newcastle upon Tyne to Hull (part of a longer route) but wanted to follow more of the coast, as the Euro-Velo 12 route does, than what Cycle Travel suggested. Therefore  I added a point at  Scarborough which is on the EV 12 route. The Cycle Travel route maintains the original route to Hull but adds a section back to Scarborough. 

How can I adjust the route so that Scarborough is on the route to Hull not in addition to the route to Hull?I only have an iPad or iPhone to do my route planning, Using the tool on a desktop seems more flexible but not an option since I’m on a 4 month bike tour. 

Thanks.