Drivers window

Okay, help needed. I’m young widow who is tired of asking guys for help who generally don’t follow through. So I’m learning the basics here. Driver’s power window didn’t work when I bought truck, ordered a new regulator, after I removed door panel and the old window regulator to install a regulator I was set and ready to install new one. However, I found a part that was just laying inside the panel gap.
It seems that it should be attached on panel for the glass? Just unsure of where it fell from.