1. On flash
2. Press mode until the M symbol appears on the top left. The ETTL shloud dissappear and the flash comp symbol wil be replaced by the 1/1
3. Press the SEL/SET button and the 1/1 will flash
4. use the + and - to set in the flash power in 1 stop increments (1 to 1/64)
Hope this helps. You need to read the manual more carefully its on page 19