The simplest way to go about it is with autocomplete (which you'll find in the ride edit tools in the bottom centre of screen). You might need to back up a bit to give the track room to connect up, but play around with it and it works well, you'll find it. You can re-edit the track afterwards .. to drag it to a new shape if you want to.
Have you started a 'new' conne express ride by the way? Suggest you don't (though it sounds like you might have) as you can add multiple stations in a single track ride, and I'm pretty not sure you can join two different rides together.