How to tighten the loose focus ring on Canon lens?

I have an EF 24-105mm f / 4 L IS that is 'well broken' with a very loose zoom ring. When the camera is pointed down, as it is when hanging on a strap or neck strap, the front of the lens fully drags to the fully extended 105mm position.

I use a plastic bracelet stretched around the lens body with part of the width of the bracelet on the zoom ring and part of the width on the stationary part of the lens body. The band provides enough resistance to prevent the zoom from dragging due to gravity. The amount of the band in the zoom ring and the amount in the barrel determines how much resistance is added.

The same type of band can be used to give a focus ring more resistance. There is even a company that markets such bands specifically for camera lenses, but I have never tried them because they appear to be the same as the rubber bands I already have for me.

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The TS-E 24mm f / 3.5L is a slightly smaller diameter (approximately 78mm) in the focus ring than the barrel of my EF 24-105mm f / 4L IS (approximately 83.5mm). The TS-E 24mm f / 3.5 L II has a slightly larger diameter (approximately 88.5mm) than my EF 24-105mm f / 4L IS. I would hope that you could easily find a generic plastic / rubber bracelet of the type used to promote charities and companies that cater to any one of them.

From a comment by the OP to another answer:

I bought this lens a few months ago (new). I think it is, but I find it strange that it is so loose by design.

The focus ring of all Canon TS-E lenses that I have handled is fairly well damped without being stiff. If the lens is under warranty, I would not hesitate to contact Canon Service. If you send it to them and they tell you there is nothing wrong, at worst it is out of the shipping price.