Adding markers to Navionics IPhone app

I have the Navionics app for my IPhone and would like to add a marker by inputting Lat and Lon coordinates. I know how to add a marker if I am physically at the spot I want to mark, but what I want to do is to add a marker to a lake while I am at home. I have a route, on my app, of the lake in question.



I have searched this forum but can't seem to find where this question has been asked.



Thanks in advance for your help.



Charlie