Stoves 900 ef heritage doubel oven. I cannot seem to get the oven to work as my daughter has fiddled with the clock which has to twisting knobs - one saying cook time and the other saying start time. I need to know how to undo whatever she has done (presumably set the timer) so that I can just use the oven manually. Any ideas???

For the 720ef , this is what you need to do. Hopefully this will translate to your 900.
There are five buttons on the clock panel and from left to right they are:- Minute Minder, Cook time, Ready Time, Plus and Minus.
TO SET THE TIME OF DAY
Press the Cook Time button and the Ready Time button simultaneously. Use the Plus and Minus buttons to set the time.(24hr clock).
TO SELECT AN ALARM TONE.
Press the Minus button to listen to the first tone. Release it and press it again to listen to the second tone etc (3 tones)
Releasing the button after the tone has sounded will automatically set that tone.
SETTING THE MINUTE MINDER.
Press the Minuter Minder button and either the Plus or Minus buttons simultaneously to set the time.
You can cancel the timer at any time by setting it back to 00.00 by using the Minus button.
After setting, the display will revert to the time of day, but by pressing the Minute Minder button again, the display will show the remaining time.
To reset the cook time, use the plus and minus buttons to set it to zero.
To cancel the automatic setting and return the oven to manual operation, press the COOK TIME and READY TIME buttons simultaneously.
I hope this helps.