You can add the module area inside the Header or in any position from the TemplateToaster and can add the modules in it from the Joomla backend,
to add the module:-
open your Project in templateToaster -> Go to module position options -> click on Widget Area option then select the position where you want to add module(in case of header choose header) -> You can set the name of the module position to recognize it in Joomla or the default name is given to that module position -> Export and install.
to Add the elements from Joomla:-
after installing the theme -> Click on the modules option -> new -> then you can add the element by selecting from a list or if you want to add your custom elements then choose "custom" from that list -> add the element you want -> select the position of your module by its name as you set it from TemplateToaster -> save.
and if you have any issue regarding this you can raise the Support ticket from the link below.