Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
I can try to help you with finding a manual, but it shouldn't be necessary -
call forwarding is not a function of the telephone (that is only true for multi line business phone pbx type systems),
rather it is a function provided as a service/feature by your telephone company
I'm assuming you may have Virgin telephone,
if so, while you dial *70 then the desired forwarding number to engage the service, you only need to dial #70 to disengage. You don't dial anything after #70, as that could start a new forward order or confuse the system.
For your reference though, I am uploading a copy of your manual here,
note I'm assuming also that your phone model is the S685, which would be the proper model name of this system (it is always based on the base station, what you sent is the handset model)