Reboot is just powering it down and then up again.
Do you mean factory restore? Reload the OS, add your user settings again?
If it was dead, did you try plugging it in to a power source and letting it sit for an hour before turning it back on? That can help.
By “dead” I meant nothing I would do normally worked to bring the iPhone XR back up. I had to do the audio buttons plus push & hold routine to force an “apple logo” restart.
Battery was at approx 50%