The treatment of a jellyfish bite is aimed at: alleviating the local effects of poison, preventing further discharge of nematocysts and controlling systemic reactions, including shock. In severe cases, the most important step is the stabilization and maintenance of vital functions.
Oral or local analgesics, 30-second use of homemade vinegar (4–6% acetic acid) can be used to prevent further spread of nematocysts remaining on the skin.  Conversely, the use of alcohol, methylated alcohols and fresh water should be avoided, as they can contribute to the release of nematocysts; It is also necessary to avoid dressings with immobilization under pressure, as studies show that it stimulates the additional release of venom from nematocysts.
Most often, a jellyfish bite does not require special medical care, unless it is a large area of damage, the appearance of a strong allergic reaction with tachycardia, difficulty breathing.
What to do with a jellyfish bite?
It is still being discussed which method is most suitable for removing tentacles, since these procedures can stimulate the further release of nematocysts . You need to immediately get to dry land and, without touching the faulty place, sprinkle it with salt water , and use tweezers to remove the tentacles . Using, say, a plastic card, a razor or a knife to extract the sting. To do this, objects should be held, pressing to the body at an angle of 30º. Tentacles can also be removed with bare hands, but it is better to immediately wash the rescuer's fingers thoroughly to prevent secondary bites. After removing all tentacles, the wound is washed with warm water, ice can also be applied, as it slows down the diffusion of the poison, thus acting as a painkiller, while the mechanism for alleviating pain from warm objects is still under discussion. Some authors argue that heat can modulate pain receptors, which leads to a reduction in pain.
It has been reported that high doses of intravenous ascorbate reduce pain 10 minutes after administration. Vitamin C is said to be effective against various toxins. 
Immobilizing dressings for the jellyfish bite site remains controversial and is considered potentially dangerous , with some not recommending it as a first aid tool. A significant amount of poison can remain in the nematocysts that have not yet been released, which have adhered to the patient's skin, and the pressure of the dressing can stimulate the extrusion of the poison from them. 
How to handle a jellyfish bite? Antihistamine ointments and sprays, oral agents will help relieve itching and irritation, after which you can apply a gauze bandage. It is recommended at this time to drink a lot.
Jellyfish bite remedies
From jellyfish burns, you can apply ointments and creams based on corticosteroids: Akriderm, Triderm, Belogent, Celestoderm, etc.
From tablets, you can use the following antihistamines: citrine, edem, diazolin, suprastin. 
Research on topical inhibitors as effective measures to prevent jellyfish bites continues and looks promising . Skin inhibitor cream (Safe Sea®, Nidaria Technology, Zemah, Israel) is already available in many countries of the world, provides protection to swimmers from jellyfish bites. This drug was recently developed as a waterproof sunscreen containing octylmethoxycinnamate and zinc oxide, which allows you to inactivate jellyfish and protect against sunburn. Due to its water-repellent properties, jellyfish find it harder to attach their tentacles to the body, and the chemicals contained in it block the release of venom from stinging cells. But he does not help after the bite of a jellyfish.
Can I swim after being bitten by a jellyfish?
Depending on the state of health and the condition of the skin, you can decide to swim or not. Slight water does not hurt a minor defeat, and therefore, there is no need to lose a day without water procedures.