1. Open Photoshop.
2. Click the "File" menu, select "Open", and select the picture to edit in the pop-up window.
3. In the Layers panel on the right, double-click the background layer to convert it into a normal layer.
4. Use the selection tools such as "Quick Selection Tool" or "Wand Tool" to select the area where the volunteer vest is located.
5. Right-click the inside of the selection and select the "Fill" option to fill the selection with colors.
6. Use the "moving tool" to move the volunteer vest to a suitable position.
7. Adjust the size and angle of volunteers' waistcoats to make them fit the body.
8. Select the "Image" menu in the top toolbar, then select the "Adjust" option, and use tools such as "Brightness/Contrast" and "Levels" to further adjust the picture.
9. Finally, just save the modified picture.
It should be noted that using Photoshop to edit pictures requires a certain level of skill, and beginners can refer to relevant tutorials for learning.