Step 1: Log into your cPanel account.
Step 2: Open File Manager option and navigate to the Document Root of the website.
Step 3: Edit the wp-config.php file.
Step 4: Enter the below line above where it says /* That’s all, stop editing! Happy blogging. */.
define( ‘WP_ALLOW_MULTISITE’, true );
Step 5: Save the file and go to WordPress dashboard.
Step 6: Now click on Tools > Network Setup.