To address this issue, you can follow these steps:

1. Remove any items from the shelving unit.
2. Carefully peel off the loose plastic piece from the shelving unit.
3. Clean the surface of the shelving unit to ensure it is free from any debris or adhesive residue.
4. Apply a new layer of adhesive or tape to secure the plastic piece back onto the shelving unit.
5. Press the plastic piece firmly onto the shelving unit to ensure it adheres properly.
6. Allow the adhesive to dry or set according to the manufacturer’s instructions.
7. Once the plastic piece is securely in place, you can reload the shelving unit with your items.

3M double-sided tape is a great option to use for securing the plastic piece back onto the shelving unit. It provides strong adhesion and is commonly used for various applications. You can find 3M double-sided tape at most hardware stores or online retailers. Just make sure to choose the appropriate width and length for your specific needs.