How can I thoroughly remove the stains on the old book cover?

1. First take out the old schoolbag, as shown in the figure below.

2. Prepare a basin of clean water and add detergent, as shown in the figure below.

3. Next, just soak the old schoolbag in the basin, as shown in the figure below.

4. The bottom of the schoolbag can be cleaned, as shown in the figure.

Next, brush off the stubborn stains on the schoolbag with a toothbrush.

6. Next, rinse the schoolbag with clear water and rinse it clean.

7. Finally, the stains on the old book bag are thoroughly cleaned, as shown in the figure below.