You need to put in the access code 8088 I think. Looks like holding two buttons down for 5 seconds gets you into the device to put in the code . They toggle until you see the upper left corner blinking. Switch to ECO
It is still going to go 10 or 11 mph in eco mode, I think. I run in eco mode as it feels more natural to me. it does start up slower. You can run the battery lower to go a bit slower. Go for a ride starting at 60% battery? I too wish my Magnum went a bit slower, but have gotten used to it after some months riding it.