@Simon-James-Hancock When you start a route on the Garmin it will ask you where you want to begin the route and it will show you all of the via points for you to choose from, and it will also give you a "Nearest Point" or something like that.
Bear in mind that it will calculate its own route from your current location to the via point that you select which may or may not be the same route that you had planned originally.
For example if you had via points A, B, C,D and E and you were between C and D and started the route and told it to start at D, the route that it calculates between your current location and D may be different than what you had originally planned between C and D. Once you get to D it will follow your route to E.
I always turn auto-recalculation off to keep the Garmin from modifying my route as much as possible.
If you definitely wanted to continue your original route exactly between C and D, I'd just make sure that my original track was visible.
Sorry this response is so late but I just noticed that I didn't submit it! Old timer's disease you know!!!