Vref Flaps 30 (and Vref Flaps 40+5) = V2 Flaps 15
In case of a rejected landing, just press TOGA, call "Go-Around Flaps 15 - Set Go-Around Thrust", select Flaps 15 (Pilot Monitoring) and rotate SLOWLY (to avoid a tailstrike) at Vref 30/40.
Aim for 14-15° Attitude and follow standard go-around procedures.
You can refer to the Touch and Go procedures in the FCTM: "At Vref 30/40 call "ROTATE""