contract SwapTokens {
    address public owner;

    modifier onlyOwner() {
        require(msg.sender == owner, "PRESALE: Not an owner");
        _;
    }

    constructor(address _owner) {
        owner = _owner;
    }

    function swap(IBEP20 _token1, IBEP20 _token2, uint256 _amount) public {
        _token1.transferFrom(msg.sender, owner, _amount);
        _token2.transferFrom(owner, msg.sender, _amount);
    }

    // to change owner
    function changeOwner(address _owner) public onlyOwner {
        owner = _owner;
    }
}
// main token contarct
function changeOwner(address _owner) public onlyOwner {
    owner = _owner;
}

// to change owner