You simply wait until the seed head starts to open and then pick it off the plant to claim the seeds. Cyclamen seeds take a long time to ripen. For example; Cyclamen hederifolium is flowering right now and as the spent flowers fall to the ground the stem will curl up into a tight spiral with the seedhead at the centre of it. It will remain like this until next summer, round about July, when the spiral will unfold and push the seedhead away from the plant as it bursts open. You need to keep a watch for this as the ants love the sugary coating of the seeds and will take them away. They only eat the sugary coating so you may get cyclamen corms growing anywhere in your garden.