how do i connect a second cable where would one go

As above, the tuner should havea cable from LNB port to it directly. You should not split a feed.

Until you arrange for new cabling/lnb, you can connect cable to Tuner B, and set tuner A = loophtough to Tuner B. (You cannot connect to tuner A and then use loop through)

Quote from abu baniaz

You cannot connect to tuner A and then use loop through

Should add that this is an issue/limitation on Solo2 and TM Nano 2 Super. On other receivers it works both ways.