Boil water. Toss a whole peeled onion and a few chopped garlic cloves. Do not add salt.
Cook the octopus for 40-60 minutes.
The cooking time depends greatly on the octopus itself. Fresh and for 20 times you will have time to boil, but with defrosted and for 60 you can go out. Therefore, in addition to time, you need to focus on the state of the octopus-cook until it becomes soft.