When you open a contact, then in the Helpdesk tickets tab there is It should appear here in the red mark.
To fix the problem, you have to apply two steps.
Firstly, please make sure that the Helpdesk module is enabled for the particular project. It could be done in the project settings.
The second thing is to make sure the correct tracker is set for the project where the contact is located. You have to go to project - settings - helpdesk tab. And here please set the right tracker on the Ticket tracker field.
Afterward, the New ticket button will appear successfully in your contact menu tabs.