* The PCM (Powertrain Control Module): This is the closest thing to a "computer" in your van. It controls the engine, transmission, and other major systems. You can't "reset" it in the same way you reset a computer. However, disconnecting the battery's negative terminal for about 30 minutes will often clear out any temporary problems or stored fault codes. This is often referred to as a "battery reset" and might solve some issues. Be aware: this will reset your radio presets and possibly clock settings.
* A specific system: If you're having a problem with a specific system (like the radio, power locks, or windows), the "reset" procedure will vary drastically depending on the specific system. Consult your owner's manual for instructions on resetting individual components.
* Clearing Trouble Codes: If you're experiencing engine problems, you might need to have the trouble codes read and cleared with a scan tool by a mechanic or using an OBD1 code reader (OBD1 was used in 1993). Simply disconnecting the battery won't clear these codes in all cases.
To summarize: There's no single "reset computer" button or procedure. Disconnecting the battery for a period is the closest equivalent to a "reset," but it only affects certain aspects of the vehicle's electronics. If you're having a specific problem, please describe it for more tailored advice.
