Depends on the model but from memory there is a small toggle or "flick switch" somewhere in a spot where it cant be easily seen (ie not obvious & not on the front panel). When you flick it "on" it will allow you to enter programming mode. (very possibly under the front top panel).
Thats if its "electronic". The "later" "auto timer" models also had a touch pad so they looked similar to an electronic touch pad model but the system for that was different..it escapes me at the moment but I think you turned a kind of adjustable thingamajigger that stuck out of the touch pad.
I did say... "from memory" *;) !
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