Cannot find Keywords tab

So following some advice from Amazon I want to add some keywords to my listings i have followed this:
o add Search Terms:

1. On the Inventory tab, click Manage Inventory .
2. Click Edit , which is to the right of each product listed.
3. On the page that opens, click the Keywords tab and enter your keywords in the Search Terms box.

But cannot find Keywords tab to enter my keywords in the Search Terms

Could someone eplain where this is please.

Thank you