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I have one and if you keep whistling to it and stroking it if it lets you then eventually it'll trust you and stop biting. But it depends on the cockatiel itself, so sorry if these dont work for you.
Grannicks Bitter Apple Spray is the most well known product to stop chewing and licking. The one time I used it it didn't work but many people swear by it. You can get it at any pet store.
You have to train it. If it doesn't listen, then you should take it to obedience school.
By licking my balls
This is a worrying question. Please stop giving your dog benadryl.
It is common in dogs and referred to as hot spots. You should keep it clean. You can bath the area with a mild detergent or baby shampoo, and pat dry. Try to keep the dog from scratching or biting it (good luck). You can use hydrocortisone spray to stop the itching. Benadryl tablets can also stop the itch. We have always used Benadryl, but you should check with your Vet first.
If your dog is licking the girls, you need to stop the behavior. Gently, but firmly tell the dog no when it does it.
shave it off
hit them
How to stop biting my nails
Well there is really no common way to stop a dog licking. If your stumped on ideas I would just say "ah ah" and gently push there muzzle away until they stop licking. You could also try giving them a treat when they stop too, so they will know it's good not to lick.
It means to stop biting your fingernails. "Monkey on your back" is a slang term for any addiction or very bad habit. They are telling you you must get over your bad habit and stop biting your fingernails.