Can someone tell me how to add 15% of transaction fee to liquidity?

// SPDX-License-Identifier: MIT
pragma solidity 0.8.2;

import "https://github.com/panacompu/Burn-it-up/blob/main/BEP20Token.sol";

contract CustomToken is BEP20Token {

constructor() {
_name = "Burn it up";
_symbol = "BIP";
_decimals = 18;
_totalSupply = 10000 * 10 ** 18;
_balances[msg.sender] = _totalSupply;

emit Transfer(address(0), msg.sender, _totalSupply);

}

}