To enable exec() function, you need to remove it from the following line in your php.ini file:
disable_functions = "show_source, system, shell_exec, exec"
1. Open your php.ini and find the following section:
2. Remove exec from the line and click on Save Changes:
3. If you need to disable show_source, system or shell_exec as well, just add them back to the line and save the changes.