Optiplex 760 MT with only one possible hard disc?

Hello together,

I am new here.

Saturday I received my "new" refurbished Dell optiplex 760 Miditower.

I wanted to include a second hard disc.

It seems this Dell is prepared with a second Slot for the hard disc - but no possibillity to connect a second hard disc to the motherbord. I found a Manual in the web. Here is only Slot 0 named as the one for the hard disc. no second possible?

Can anybody help me?

( I am not a professional - but since 1986 when I had my first XT PC I was work a lot on and with them . . . this would be the first with only one possible hard disc . . . )