On a standard motorcycle, the left foot operates the gear shifter by lifting up and pushing down with the toes.
Riders with ankle problems or a BK prosthetic can modify the shift lever by adding a heel extension to allow changing gears by both pushing down with the heel and pushing down at the toe position.
This system already comes standard on some cruiser models like the Harley Davidson.
Alternately, the shifter can be moved to the right side as it used to be on older British and European bikes.
A slick newer option is the electronic shifter systems. The Kliktronic for example is a gear-changer that uses a push button gear selector on the handlebar connected to an electric solenoid to operate the bike’s shift lever. Gear changing is done with the left hand, and the very complete kit can be moved if /when you change bikes.