Always use a syringe or grease gun when attempting to repack bearings with grease. You should keep the work environment clean and be careful not to mix greases as not all are compatible. Make sure to work the grease between the balls and then rotate the bearing several times so that every metal-to-metal or ceramic-to-metal surface is lubricated.
After refitting the seal, wipe the bearing’s outer surfaces with an oily cloth to protect against corrosion (unless the bearing is stainless steel). After reassembling the bicycle, check the performance of the freshly serviced bearing. If you hear a crunching noise while turning the axle, dirt has found its way into the bearing. Unfortunately, you will need to start the cleaning process again.