Magento2 InstallSchema.php does not create the table specified

The installer won't run again if it was already executed.
Removing the record from setup_module with module = 'MyVendor_Helpdesk' should make it run again.

please try the following code.

delete from setup_module where  module ='module_name';
sudo bin/magento setup:upgrade
sudo bin/magento setup:di:compile
sudo bin/magento cache:clean

if you get any permissions errors on var folder.

sudo chmod -R 777 var/*