how can i fix my zanussi washing machine?

how can i fix my zanussi washing machine? the spring that's inside the door that keeps the rubber seal round the drum come of, and i don't no how tho get it back on.....at the moment i can not use my machine as the drum moves when its on a cycle and water spills out of it..... can u help? I'm a able to fix this myself? or do i need to get a professional in? many thanks