A simple smart-contract with 2 methods to read and write a private variable.

SimpleStorage.sol

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

import "@openzeppelin/contracts/access/Ownable.sol";

contract SimpleStorage is Ownable {

    uint64 private _storage;

    function set(uint64 input) public onlyOwner {
        _storage = input;
    }

    function get() public view returns (uint64) {
        return _storage;
    }
}