1. Gather your tools. You will need:
* A screwdriver
* A pair of pliers
* A valve guide
* A valve spring
* A valve cap
2. Remove the valve cap. Use the screwdriver to pry the valve cap off of the valve.
3. Remove the valve spring. Use the pliers to compress the valve spring and then remove it from the valve.
4. Remove the valve guide. Pull the valve guide out of the valve.
5. Clean the valve. Use a soft cloth to clean the valve.
6. Replace the valve guide. Insert the new valve guide into the valve.
7. Replace the valve spring. Place the new valve spring over the valve guide and then compress it with the pliers.
8. Replace the valve cap. Use the screwdriver to screw the valve cap back onto the valve.
9. Test the valve. Play the trumpet to make sure that the valve is working properly.
If you are unable to fix the loose valve yourself, you may need to take your trumpet to a qualified repair technician.