toilet handle?

The section of the handle spindle inside the cistern is square on this there should be a plastic arm with hole in end to take the hook from the syphon replace the hook in to the plastic arm gently squeeze it closed to stop it falling off again. If the arm has broken you will have to get another but might have to purchase the complete handle assembly. Easy job and you don't have to turn the water off.
If the plastic arm has come off the spindle then slacken off the screw that should be over the square hole replace [hole is square to fit spindle] then re-tighten the screw on to the spindle. If the arm is not on the hook have a look you might find the plastic arm at bottom of cistern or floating around check it's not split at hook end [hole] or the spindle end [square hole]

Bob
June 2010