I had a small hole like that, squeezed in some white geocel and left it to set up. Then took a one sided, new, razor blade and shaved off the excess a couple days later. Big enough blob on the inside to adhere and no painting needed.
You could put a piece of blue tape over the hole, make a hole in that and force in the geocel. Let set up, razor it and pull the tape but my hole was BB size so just put the nozzle up there and squeezed it in.
2017 SLX 195RB
2021 Jeep Grand Cherokee Summit L 5.7L V8
Andersen WDH hitch, Renogy 100 AH Lithium &
200 Watts solar panels from Renogy
Prev. '14 Jeep Grand Cherokee Overland, gas 3.6 V6