These are seed pods. You can let them mature and try growing the seeds: https://www.gardeningknowhow.com/ornamental/bulbs/amaryllis-hippeastrum/amaryllis-bulbs-propagation.htm

But, be aware that if you leave the seed pods on, the plant will have a smaller flower the next time it blooms due to the fact that the bulb will be splitting its energy between the seed pod and next year's flower. If you do not want to get seeds, you can simply cut the flower stalk off.