lens – How to reduce shake at high focal lengths {2600mm-3900mm with adapters} when on a tripod?

I have a Nikon DIGITAL DSLR 650 1300mm zoom lens. In honour of this, I bought a Zomei tripod which is of good quality but even so, the slightest breath of wind makes the lens shake, and at such high magnification, there is an obvious effect to the image. Am I supposed to live with this? Or is there a way around this? I have seen a weight, actually a sandbag, that can be suspended on a hook provided on the bottom of the tripod’s vertical mounting tube, but my nearby, long established camera shop in Stafford had no idea what I was talking about and are currently on lockdown anyway.

Assistance would be great with this.