My token contract erc20Burnable and second contract for staking and all function perfectly fine but burn function. As you know, IERC20 Interface doesnt have burn function, how to add a burn function to my staking smart contract? how to use burn function (like token.transfer()) in IERC20 Interface?
You could import your token to interact with it, or you could create a new interface containing the functions you want to call (including burn) and interact via the interface.