Amending the page associated to a Category link

[3bsstudio]

(osCommerce 2.2-MS2)

I'm going mad and cannot for the life of me work out how to have the Category link in the menu go to a page I have created.

The daft thing is, I did exactly the same thing a few months back and it worked but I can't remember how I did it.

What I want to achieve is the same as this page: https://www.gasbottlesdirect.co.uk/air-products-industrial-gas2-c-1017.html 
which I went through the same process - the category was added, I created the page copy and it got inserted into the category page link - but I can't remember how I did it????.

I want to do the same with this page: https://www.gasbottlesdirect.co.uk/hobbyweld-hobbybrew-gas1-c-105702.html
I have created the page copy here: https://www.gasbottlesdirect.co.uk/hobbyweld_hobbybrew_online.php but I don't know how to get it to appear in the category page https://www.gasbottlesdirect.co.uk/hobbyweld-hobbybrew-gas1-c-105702.html

Can someone please put me out of my misery? Apologies if I'm being totally thick but I just can't remember how I got the page copy into the dynamically generated page.

[bonbec]

Hello,

Not sure to understand. The copy page is, in your admin, under the categories list ?

If yes, select this page and in the right of your screen, you can see a move button.

Click on it and choose the right category in the select list.

See the screenshot (sorry, I am french and my shop is only in french language)

Edited June 7 by bonbec
screeshot added

[3bsstudio]

I don't have anything like that? I can move categories but I don't have any pages in a list?