This is a very basic model home phone, and because it is a single line system, it is not capable of call forwarding.
Business systems can do call forwarding because they typically have multiple lines available.
That doesn't mean you can't forward calls, it just is not a function of your ATT hardware.
Rather you would do this as part of a feature/service provided by your phone company.
On most, but not all, phone companies will permit this so long as it is part of the service you subscribe to, and most engage call forwarding by picking up the line, get a dial tone, and key in *72, followed by the number you want calls forwarded to, then hang up.
To cancel it, dial *73 from the home phone.
If this does not work, it doesn't mean you can use forwarding, just that you have to call your phone provider and ask them if the feature is enabled and what command/code they use to program the forwarding.
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