Firstly you need to load mod_reqtimeout Apache module.

Login to your Plesk Panel.

Navigate to Server Management > tools & settings > apache module select reqtimeout module.

Then look in your httpd.conf your should found this line below.

LoadModule reqtimeout_module /usr/lib64/httpd/modules/

Add this line below to httpd.conf

RequestReadTimeout header=20-40,MinRate=500 body=20,MinRate=500

Then restart apache service.

service httpd restart