Power steering pump is not working and i need to replace it but sumone side i need to reset ecu how do i do that its 2001 1.4 peugeot 307

The ECU shouldn't have anything to do with changing your power steering pump. If you want to reset it and definitely need to change the pump, Kill two birds with one stone. Disconnect the battery while you change the power steering pump. When you're finished changing the pump, sufficient time will have elapsed so that when you reconnect the battery, the ECU will be reset. Just bear in mind that when you do this, any devices that use a memory (radio presets, clock, etc.) will need to be reset to your preferences.