Reset service light Citroen

Find how do you can reset service light or turn off board light maintenance indicator when errors like, oil change, check engine, change intervol of inspection, airbag light, inspection key, when maint reqd, appear on board computer display. For Citroen car models, Citroen Xsara Picasso, Citroen Saxo, Citroen Xsara, Citroen Piccaso, Citroen C2, Citroen C3, Citroen C4, Citroen C5, Citroen Xanita, Citroen Synergie, Citroen Dispatch.