I hope that you uninstalled .194 via the PC's Control Panel, Add or Remove Programs.
Once you have done this and installed .170 then when you run Application Loader in DM it should pick up and ask if you want to downgrade.
Did you get the version of .170 from the AT&T link that I gave you?
If .170 is really installed and DM really will not install it then unzip the little file I have sent you, connect your phone to the PC and launch the file.
It will wipe (brick) the phone and install the new OS but there MUST be an OS for it to install so please, please check this in Control Panel, Add or Remove Programs BEFORE you run it. It will not do a backup first.