The mind is always looking for threats. When you practice thinking of things to be thankful for, you retrain it to notice advantages.
This takes time and repetition but it does work:
When you wake up in the morning, think of ten good things and count them on your fingers.
Here’s an example: Thank you for my car. Thank you for my toothpaste. Thank you that I'm not in a burn ward receiving skin grafts... Get creative but don't be sarcastic.
Who are you thanking? Everyone and everything involved in making these good things possible.