Besides the traditional way of packing bearings in your palm, found a tool like this helps to pack the bearings. You can check to see the old, then new grease come out each roller. Takes some pressing and rocking of the handle but it worked.
https://www.amazon.com/gp/aw/d/B0B1M...4505EPYW&psc=1
This one that connects to a grease gun works similarly and actually has better reviews.
https://www.amazon.com/gp/aw/d/B0931...5O08GT8E&psc=1