How to spray silicone onto the drilled ventilation pipe?

Hello.
A hole was drilled into a ventilation duct of the controlled residential ventilation system when the holes for fastening a handrail were drilled. An 8mm drill bit was used. The ventilation system manufacturer recommends installing a sleeve and chiseling out the wall or injecting silicone into the drill hole. Since we do not want to have a major construction site again in the new building, I would like to plug the pipe with silicone.
Now I am wondering how to best get it into the pipe with 8mm drill holes and a depth of about 6cm. Does anyone have an idea? I only know the usual nozzles for silicone cartridges.

Who drilled? If it wasn't you, I would hold the person responsible accountable. Take a look in the [großem Fluß] for thinner tips. Whether you are directly on the pipe or just before it shouldn't matter with a solid wall.

and otherwise you just have a "mini-valve" in an unplanned spot. Our plumber once said that it’s not a "broken leg." How to take that exactly, I can’t say. Air just comes out at an unplanned place – nothing more and nothing less

Take a drinking straw (one of the good plastic ones). Then put it into the hole and squirt the silicone in place. I wouldn't worry about the air, but condensation can also form, and that shouldn't get into the wall. (Why is the pipe even in the wall?)

Is the hole actually going to be used for the handrail now? Even if a plug with a screw is inserted there, it is basically sealed. The air that still passes through is negligible.