If its still in the powder form and you haven't rubbed it in the easiest way is to carefully lay some sellotape on it and then remove and the pollen will stick to the sellotape. If you have already rubbed it in then I dont think this will work and sorry but don't know what you can do
Try one of the oxygen cleaners. Here in the US we have one called Oxi Clean. Make a paste and follow the directions for stain removal. These cleaners are great for getting out organic stains.
Good luck,
Newt