How Do I Bring An App Back To My iPhone’s Home Screen?

I have iPhone 12. Prior to this I had a 6S Plus. I used to be able to rearrange all of my apps on my iPhone via iTunes on my Mac. However, I can’t seem to do that anymore. What am I missing here? I know I can back up my phone to my Mac via Finder and I can see all of my music on the music App of my Mac. But I can’t access the content of my iPhone, i.e. all of the Apps. Thank you for your help.
The reason I want to be able to do this is because somehow or other I have deleted my WhatsApp icon from the iPhone, however, the App is still in the iPhone itself (I can access it via the search function) but I want it back on my screen. From all of my research the only way I can get all of my Apps back is by resetting the home screen layout. I don’t want to do this because all of my folders will be deleted and I’ll have to go back a recreate them!
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Ruth Keeble