I would strongly advise against using the metal tray that had the plastic bag melted onto it in the oven again. When plastic melts and adheres to a surface, it can release toxic fumes and chemicals that can be harmful if ingested or inhaled.
In this case, the plastic bag was subjected to high heat for an extended period, resulting in it melting and adhering to the metal tray. Even if you have managed to remove the visible plastic, there could still be residue or particles of plastic left on the tray that can contaminate your food when exposed to heat again.
To ensure the safety of your cooking and avoid any potential health risks, it is best to replace the metal tray with a new one that has not been exposed to melted plastic. Using the contaminated tray again could result in the release of harmful substances and compromise the quality and safety of your food.
If you are uncertain about whether the tray is safe for use, it's better to err on the side of caution and replace it to avoid any potential health hazards.