how to refit a timing belt on a renault scenic 2000 K4M engine?

The timing belt had not snapped, but the crankshaft pulley had come loose and I assume the timing belt had jumped a tooth - but I have 4 bent exhaust valves on cylinders 3 and 4, I have stripped the engine down and had the head skimmed, have bought new valves and have bought the timing tool, but am confused about what timing marks I need to reset the timing, I have the haynes manual but find it confusing. Any advice please.