The Signalink has no capability of sending CAT signals to the IC7000 or any other radio.
To do that you will need a Serial USB adapter to convert the output from the PC (USB) to TTL level serial, with the RX and TX as above.
There are a number of them available on Amazon and Ebay, etc.
One can modify a Beofeng programming cable to work by again tying the RX and TX to the tip of a 3.5 MM plug.
You can also buy a cable expressly made for the Icoms.
You can manually set the frequency to that specified in the WSJT-X program and set the split operation to NONE and work without the CAT.
No cat, no cat control.
You still need to get the signal in and out of the radio and out and in the PC.
The Signalink will still operate the PTT through the 6 pin MiniDin cable.
For the whole thing to work you will need that CAT converter.