Different menus on different pages

Hey there, I am fairly new to the whole topic of WP theme customization (means also a coding newbie with sadly no experience in PHP). However current situation is that I have a landing page with the primary menu that shows all current links and pages that have been added - since the website splits into 2 different topics, I am looking for a way to keep the whole menu on the landing page while the subsites only have their own sites in the menu along with contact and privacy policy. Thank you for any help in advance Sincerly