The exact directions for refilling a pepper grinder vary depending on brand and design, though most involve removing the grinding mechanism to access the inner chamber. Once the grinder is off, pour whole peppercorns into the chamber until they reach the top of the container, Then replace the grinder.
Most manual pepper grinders have a basin that holds the whole peppercorns and a grinding mechanism with at least two moving parts. To refill this style of grinder, hold the device so that the grinding mechanism faces upward, otherwise peppercorns and pepper debris may fall out during the process. Locate the adjustable portion of the grinding mechanism and twist it in the direction for a less fine grind until it comes off. Pull off any other loose parts until there is unobstructed access to the main chamber. Pour in the desired variety of whole peppercorns until the container is full, and then replace the loose components in the reverse order.
Many models of mechanical grinders feature a separate detachable section to the peppercorn container, as the grinding mechanism usually doesn't contain any removable parts. This section is typically found on the base of the container. Some manual models, such as the Oxo pepper grinder, also have a removable base.