This is an overview regarding loose tuning pins.
NOTE: this is one possible repair… the repair method used may vary depending on your actual piano.
In some cases, a more extensive repair may be required such as replacing the tuning pins with larger ones, however this has to be done in the workshop. In some cases, the pin block has to be replaced completely! Which would be a major overhaul of the piano. Replacing a pin block is not something I would do, if your piano needs this level of repair, I would refer this to Emanuel Rey.