I recently changed the solenoids in my 1992 Lexus ls400 but don't know how to reset the transmission.How do I do this

 

I haven't heard of resetting transmission, maybe you mean ECU reset. Just unplug the battery for few minutes and that should reset everything.

 

there is no seperate TCU on these cars.
an ECU reset also resets the transmission since they are in one unit.

 

Solenoids are solenoids, these cars are not like some new Mercedes that need CAN configuration after replacing the conductor plate oh I don't think that is needed on a W208 though. Now why would the tcm / ecu even care if you replaced the solenoids? As long as they are the correct ones for the year.