They should be on your phone. But to easily find them, you can go to Settings > General > Reset > Reset Home Screen Layout and the apps that came with your phone will populate first. Is there an app you think you may be missing?
Iphone 6S Plus
2 replies
In the App Store:
See here: https://support.apple.com/en-au/HT204221#names
Or
Do restore as new, see below
where do i find the apps that came with the iphone 6S Plus