Welcome to the forum JerryG.
The few times I have been to lazy (or ill...battling cancer here) to repot,
I lifted the whole rootball out of the pot, and added more Osmocote to the bottom of the pot.
Then I plopped the entire plant back into the pot, pressing the edges of the soil firmly against the rim.
I use pots without drainage holes so the fertilizer stays in the pot and doesn't seep out into the pond,
at least not without first seeping up through all the roots of the plant.
If you can not do that, try making a hole with a wooden dowl (round out the end with a rasp so there is less damage to the roots of your plant) all the way to the bottom of the pot. Sprinkle a couple of tablespoons into the hole, pushing the Osmocote to the bottom with the dowl, then fill the hole up with fresh soil, tamping down firmly, using the same dowl again.