speedo setting for smaller wheels ktm supermoto

hi guys . need help ! got a factory built ktm 625 lc4 sxc 2003 love it but speedo isnt reading correctly , been through all the menus on the speedo and , 2205 ws is displayed , and it should be 1882 or 1821 but i dont know how to enter this info into the speedo , checked the magnetic sensor in the front wheel and its ok , so if anybody could shed any light , get in touch , [email protected] thanks