How 2 unlock stereo security on my 92 GT vert

[TurboFC3s]

I just got this 1992 Celica Gt convertible and i bought it with a dead battery. When i put one in the radio display read "HELP".
i called the dealership and the said there is no user code to punch in like with other cars, they would have to reset it for me.
I looked around online and couldn't find any help.
its the double DIN tape and CD player.
Does anyone out there know how to reset the theft code so i can have my sounds back. Any info would be great.
thanx