First try unplugging the firestick and waiting for 30 seconds and plugging it back in
If that doesn't fix the issue, then try unplugging for a few hours.
If this still doesn't fix the issue, you can try some amazon remote button sequences as follows:
* Press and hold the SELECT and PLAY buttons simultaneously for about 5-10 seconds and the Fire TV will reboot.
If this still doesn't fix the issue, you can try the following this video to reset the firestick:
https://www.youtube.com/watch?v=bE8o60KLqoU