stopping the string

The lever rotates... but it also twists. It is a matter of feeling the actual movement and then finding, gently, a point of support... from where the lever will no longer move. The less consistent the lever's hold is, the more it will be necessary to accentuate this "support". By insisting on the key, the lever and therefore the string must no longer move. If the tuning, in your case, has dropped significantly, it can depend on many reasons. First of all, one must see how far the tuning was from 440. There may have been a general settling. The structure, naturally, reacts to a greater load, so try tuning again with a "confirmation tuning". If the piano is down by more than a quarter tone, it is advisable to also bring it a little above concert pitch. In some instruments that allow it, strings (especially if replaced) can be brought even 1/2 tone above, then waiting for a definitive settling. However, be careful with old instruments! Especially if they have been, for example, half a tone low for many years. Some strings, perhaps with a little rust, may break. The discussion should be more complex and supported by practice. If this is sufficient, let's stop here. Good luck with your work

Always clear and kind.

Thank you Maestro! Camillapiano