1. Put in body position to fine-tune to begin with. 2. Start with half octave (middle C upwards). Each piano key hits from one to three strings. Choose a string to tune, if there are three strings, start with the medium. Carefully turn the plug of the string you want to tune.
Put the rubber dampers to stop the vibration of other strings in the game. Proceed slowly. Stretch a string can break very quickly, especially if you are old. If the string is really out of tune, you may have to refine it in several steps, allowing to rest for minutes between each step. (Thanks to a reader for pointing this out.) For the right fit, for the left loose. If you turn the plug to the right or in the direction of clockwise, tighten the rope and this will sharpen the tone. By turning to the other side, release the rope and lower the tone. Do not force the plug.
Turn slowly, carefully, without bending. Do not move sideways in any way. Move the most delicately possible (best practice). Too much handling can release, and a loose pin will be impossible to tune. A very hard technique can lead to this. Loose plugs should be replaced by a professional. What is “to fix or stabilize a pin? Fix or stabilize a plug means moving in a way not to come out of tune. To set a pin, the last movement of tuning to be done must be to the side of the clockwise or right.