Hi
I'm afraid that no-one here can advise you whether or not your iPhone only requires a screen repair. It will need to be checked.
Contact Apple Support (mail-in service may be available), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your iPhone to be inspected and to establish your available service options, likely timescales and cost:
Repair service price information for iPhone in the US, for example, is available here:
https://support.apple.com/iphone/repair/service/pricing
The screen from your iPhone 6s cannot be used to replace the screen on your iPhone 7.
Note also that, if you have the screen repaired by anyone other than Apple or an Apple Authorised Service Provider, your iPhone may no longer be eligible for any future service from Apple (including chargeable repair).