Frozen screen on iPhone 6S

This is what Apple recommends in their support article. You already tried the forced restart, but it won’t hurt to try it a few times. If it continues to fail, try the other suggestions.

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

Try a forced restart. You say you have the 6s but the iPhone 7 is showing in your profile.

• iPhone 8 or later: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Side button until you see the Apple logo.
• iPhone 7, iPhone 7 Plus, and iPod touch (7th generation): Press and hold both the Top (or Side) button and the Volume Down buttons until you see the Apple logo.
• iPad with Home button, iPhone 6s or earlier, and iPod touch (6th generation) or earlier: Press and hold both the Home and the Top (or Side) buttons until you see the Apple logo.