You will want to ease in and start with tap water as opposed to pool water or open freshwater and saltwater. The sink should be full enough that you can submerge your face at least halfway. Avoid temperatures that shock or scald the skin with cold or hot to make the process easier. Let your face adjust to the temperature and make sure you feel comfortable and calm when you are submerged underwater. If your nose is irritated at this stage, you should stop, as your eyes are likely to become more irritated by chlorine or cleaning byproducts from halogen-based cleaners. Practice keeping your eyes open underwater as long as you can hold your breath. The temperature of the water should be moderate to cold, as in pools or the sink earlier. Continue practicing this until you have no trouble and don’t mind the irritation of exposing your eyes to water.

How would you rephrase that briefly using Indonesian?
Pergilah ke kamar mandi dan isi wastafel dengan air. Masukkan wajah Anda dengan mata tertutup. Tenggelamkan diri di bak mandi.