Copy the data on the handheld to the unit's memory card.
Transfer that memory card to the graph and load the data.
Job complete.
I'm in a similar situation but I have waypoints on my Navionics app that I want to get to my Hook2 5 (which does not have WIFI). I called Lowrance and the "tech support" guy I talked to said this is not possible unless the files on the card are converted somehow. He couldn't tell me how to do it. He said the unit won't read the waypoints from the card. Given my experience with Lowrance I take this with a grain of salt.
With the mobile app, just select the Menu button, go to Markers, touch the three dots beside the waypoint name and choose Export GPX file.
You can do the same with Tracks.