First unofficial workaround to get what you want:
You use the card to buy something. Then you sell that thing for cash. Finally, you take the cash to your bank and put the cash into your bank account.
Second unofficial workaround to get what you want:
You sell the gift card. Then you transfer the money you get for the card to your bank account.
Third unofficial workaround to get what you want:
You go to a place where things that can be bought with credit cards but not with cash. Vending machines and unattended gas stations are usually the best choices. Even if it says cash can be used, it won't take all money. (Pennies usually don't work, and some paper money is too badly damaged for the machine to accept it.) Wait for a customer who has money but does not have a credit card and therefore can't pay. Have them give you their money, and use your gift card to pay for their purchase. Finally, you take the cash to your bank and put the cash into your bank account.
You don't. A "gift card" can be used only for purchases. It cannot be used for PayPal and it cannot be used to put money into a bank account. It might not work online at all (some gift cards can be used only in person in stores that can scan the card in their machine). Even if it can be used on Amazon, then it can be used there only for purchases, and not to transfer money to anywhere else.