Wii Sports Resort Bowling does not have bumpers. Unlike Wii Sports (original) Bowling, the Resort version removed the bumper option entirely—likely to emphasize the improved MotionPlus precision.
Spend 30 minutes in Training → "Picking Up Spares". It teaches every spare combination systematically. The stamp rewards are pure skill—no bumpers needed.
Note: Original Wii Sports Bowling (in Wii Sports Club on Wii U, or disc) does have bumpers for young kids.