S and R are pre-equipped. Your dealer need to install a software enabler (P/n 61600940000) about £334. This option is standard on the Rally (Some early rally models had QuickShift+ disabled, they need a software update)
Once installed and enabled there is a new menu available to turn it on and off. The quickshifter works for both upshift (cutting power) and downshift (blipping the throttle).
If the menu is not present, quickshift+ is not installed. You can still change gear up without using the clutch if you do it at the right RPM, but this is not a true shifter that is cutting the power. Some (rare) bikes have the quickshift active but nothing in the menu: it is a factory misconfiguration and the feature may disappear when the dealer updates the software on the bike…
If the quick shifter stops working, check the clutch lever microswitch, the quick shifter is intentionally turned off is the clutch is disengaged, and the only thing carrying this information is this small microswitch (In addition have a dysfunctional switch there is potentially dangerous as it will not prevent starting the bike in gear). See this thread.