iPhone won't turn on after being dead for a month

See this support guide and follow all the steps provided:

If your iPhone, iPad, or iPod touch won't charge - Apple Support

and/or

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

If the issue still persists, it could be a hardware failure (battery? Charging port? bad cable?), but we can't diagnose that kind of problem remotely.

Make an appointment at an Apple Store or Authorized service provider and have your device inspected: Apple – Location Selector

Regards

Giulio

Most of your post is nonsense.

iPhone has a functionality that when its power off and someone put it on charge it automatically power on after having battery power appropriately 5% (varies with device to device). You just need to put your iPhone 7 Plus o charging. If you are using original cable and adapter it will take half an hour to turn on itself and if you are using 3rd party accessories it will take less time because 3rd party chargers charge iPhone quickly (but may slows the battery life). If you see that your iPhone is not turning on after having charge about half an hour then manually power it on by pressing and holding power button.

If nothing works then that mean your iPhone 7's battery has been damaged. In that case take your iPhone 7 to nearest Apple Store and get your battery replacement.