Why 3D touch is not working in my iphone 7?

Restart your iPhone, iPad, or iPod touch

If it is still not working after the restart, check out this article for some good troubleshooting steps for 3D Touch: If the screen on your iPhone, iPad, or iPod touch doesn‘t respond to touch​
Let me know if this works.
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I had a problem with my iPhone so I sent it to Apple Service in Bulgaria, from the store I've bought it. They sent it to me back after 10days saying my problem was software update. I don't know what they have done but after I got it my live wallpapers doesn't work no matter how longer I keep my finger on them, and my 3D touch doesn't work on 'Low'. Before I sent it to the service when I touched the screen the live wallpaper moved even if I pressed a slightly pressure. Could you help me what can I do? I can't sent it back to Apple service because I work with my phone and the first time they didn't even gave me some sort of phone to use. So, please help me!

my iphone 7 plus 3d not working

hi. I alreaddy do above instruction but still 3d touch is not working. pls tell me the other option.