May I know the app you downloaded?
This ‘app’ may of downloaded malware to your device and caused the phone to keep shutting itself off.
Otherwise, try the following steps;
Step 1. Open the back cover of your Note 4, remove the battery and wait a couple seconds, then insert it again.
Step 2. Hold the volume up key, power button and the home button simultaneously. When the ‘Recovery Booting…’ text, release these buttons.
Step 3. Select the cache option and press reboot. If this doesn’t work, repeat Step 2, press the cache option, and select format device. (Note! Formatting your device will wipe your device clear of all files.)
Hope this helped!
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