Jim, your trailer has a grease fitting under the rubber cap on the hub nut cover, pop it off and you can use a grease gun and pump it up untill you see the grease start to come out from behind the nut.
I like to jack it up and spin the wheel as I am adding the grease, and it is a good time to adjust the brakes
at this time. Don't forget to use a jack stan or some good blocks for safety.
Since you have 5K on your trailer I would repack the bearings and replace the seals, get parts from Dexter axel you should have the info that came with your trailer.
I will be doing my trailer in Augest before our big trip.
I use Sta lube Hi temp wheel bearing grease and have the same grease in my lube gun, don't mix the greases . Jay