This issue occurs when user is unable to install any Plugin to manage its WordPress website. Let us go through the detailed procedure to fix the issue.
Login to cPanel account associated with your WordPress website.>>Go inside File Manager>> Now, get into WordPress domain directory and find wp-config.php file>>Right click over the file and click over Edit.>>
You will be directed to the editor page. Scroll down to last or find the below given lines.
define('DISALLOW_FILE_EDIT', true);
define('DISALLOW_FILE_MODS', true);
Modify the code from true to false.
define('DISALLOW_FILE_EDIT', true);
define('DISALLOW_FILE_MODS', false);
Click over Save Changes