Force an outbound call to use a particular Zap channel

I am trying to remotely turn off the call forwarding on an AT&T POTS line attached to an Asterisk 1.6.2 box using FreePBX 2.7.0.

Problem is it’s the 4th channel on an Astribank and I cannot physically disconnect and swap it with the 1st line/channel to be sure the *73 (toggles forwarding OFF on AT&T analog lines) goes to that line.

Can I send a *73 to that line via the cli? If so,… how?

Any suggestions would be greatly appreciated.