1. Prepare your tools and materials. You will need a cello string winder, a pair of needle-nose pliers, and a soft cloth.
2. Loosen the string. Use the string winder to turn the tuning peg counterclockwise until the string is loose enough to remove. Be careful not to loosen the string too much, as this can damage the instrument.
3. Remove the string from the peg. Gently pull the string up and off of the peg. Be careful not to drop the string, as this could damage it.
4. Insert the new string into the peg. Hold the new string with the soft cloth and insert it into the peg. Make sure that the string is seated properly in the peg.
5. Tighten the string. Use the string winder to turn the tuning peg clockwise until the string is tight. Be careful not to over-tighten the string, as this can also damage the instrument.
6. Tune the string. Use a tuner to tune the string to the correct pitch.
Here are some additional tips for fixing a loose cello string:
* If the string is broken, you will need to replace it with a new string.
* If the tuning peg is damaged, you may need to replace it with a new peg.
* If you are not confident in your ability to fix a loose cello string, you can take your instrument to a qualified luthier for repair.