Amazon sword plants usually send up a flower spike when mature (about 1 year old) and after a cooling off period. They normally flower in spring and summer after a colder winter. The same thing happens in aquariums but less often. If you let the aquarium temperature drop to 20-22C for a few months over winter, that can encourage them to send up a flower stalk when the water temp increases to 26C.
Make sure it has lots of light and fertiliser and hope for the best. However, many sword plants never send out a flower stalk when kept underwater.
If you really want to propagate the plant, grow it in a pot outdoors and in spring and early summer it will send up a flower spike about 4-6 feet long and that will have white flowers along it. These get pollinated by bees and produce seeds that can be plants in damp gravel and new plants grown up.
