Welcome to iPhone Forums!
What did you try to solve your problem?
Make sure your iPhone SE is turned on, unlocked and on the Home screen. Also make sure everything is up to date: iPhone, computer and iTunes.
Restart computer and iPhone.
With a Windows PC, follow these instructions, if it’s still not recognized:
If you connect your device to your PC with a USB cable and your PC doesn't recognise your iPhone, iPad or iPod touch, find what to do.
support.apple.com
Hope that helps.