To replace the cmos battery for a laptop you will need to completely disassemble the bottom of your computer and you should see a button cell battery on the motherboard it self.
Be very careful if you are going to attempt to change it and dont' lose any of the screws and besure you look under any panels before you remove them to insure there are no hidden wires under them taped or wedged inside to insure nothing gets damaged.
There should be a inside look based on the exact model of your Toshiba on the internet. I would point it out but not sure exactly what model yours maybe.
Find the service manual for your laptop before you do anything, will show you the location of the battery. You don't need to replace it, just take it out for a few seconds. Make sure you unplug the main battery and power.