The basic tripod has one knob to tighten or release the column and a handle to release and tighten the legs.
Mine has an extra bit.
Mine has something extra and a third knob just above the words Benbo and Trekker in the picture I posted.
I'll try and explain, please stay with me as it may be difficult to describe
Mine has an additional bracket which attaches in the same way as the legs to the bent bolt and is tightened and slackened along with them via the handle but the column is fixed to this bracket and is tightened and released with an additional knob. It's really just a flat piece of metal which is vaguely figure of 8 shaped with a couple of holes in it, one to connect on to the bent bolt together with the legs and the second to take the knob securing the column assembly.
With this extra bit fitted you can position the tripod legs and tighten the bolt and then slacken the extra knob and move the column and it's mount independently without the legs going all floppy again.
I expect a lot of people just use the tripod and never complain or worry but I have also read people complaining the tripods are too much like a drunken set of bag pipes and for those who feel like that this extra bit may help. I find it helps as when setting up I don't need to worry where the column is, I just set the legs and then position the column, separately, rather than the legs and the column needing to be positioned as a part of the same process.
If you're interested maybe Paterson Photographic can help as I think they own Benbo or are at least dealers. Here's their number 0121 520 4830 or alternatively you may be able to rustle up an email and email them.
Here's the internet link...
https://www.patersonphotographic.com/
Of course it may be that you'll be happy with your tripod just as it is
PS.
I've had mine for many years and although I don't use it much I would hate to go back to a conventional centre column through the middle of the legs design as the benbo is IMO much more flexible. Plus mine has been pretty much indestructible and does actually seem more stable than the Manfrotto it replaced.
I hope you get many happy years of use out of yours