Composer detected issues in your platform: Your Composer dependencies require a PHP version

 Composer detected issues in your platform: Your Composer dependencies require a PHP version 

Faster and quick solution 

Path: ~/.composer/vendor/composer/platform_check.php

if (!(PHP_VERSION_ID >= 70300)) {
    $issues[] = 'Your Composer dependencies require a PHP version ">= 7.3.0". You are running ' . PHP_VERSION . '.';
}

Here update/change php version id as your need