Make sure that there are no obstacles in the water below you.
Let yourself fall backwards into water.
Another type of roll is used when diving with a dry suit: Here you must turn on your own axis once under water after diving in, so that the air from the legs is distributed into the whole diving suit. This movement is very difficult though and therefore you should practise it several times before using it. Otherwise it may happen, that you are pulled to the surface of the water due to the unevenly distributed air.
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