Hi I have an iPhone 6SPlus and I can’t open it. The screen ask to deactivate iPhone with ITunes

I have never heard of anyone saying their phone is instructing them to Deactivate it using iTunes. Look Closer. It is most assuredly saying your phone is DISABLED, Connect to iTunes.

If that is correct, see this link for instructions --> If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

Does it say deactivate or disabled? If disabled, see instructions in If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

You're welcome