Welcome
I had an issue when I bought my bike from a private seller where the right turn signal would blink normally, and the left would just stay solid.
Long story short, they had an aftermarket tail light/fender eliminator and the resistor that was supposed to be wired into the circuit for the left light had detached. Just reattached it with some electrical tape and it's working fine now.
I'm no electrical engineer or anything like that by the way. Just looked at the wiring in the rear storage area and saw the loose wires and tried connecting them and presto, it started blinking. Sometimes you can spot something fishy that's causing the problem just by digging around a little!
Anywho, if you can't find out the problem on your own, there are definitely some on here that will be able to help ya!
Good luck with your new ninja.