How to reset bios on toshiba satellite l305-s5933

Are you sure you mean the BIOS as this is held on a chip on the machine.

What issues are you having with your machine ?

When you first turn on your laptop, look for the info on the splash screen that first comes up - I'm pretty sure it is F2

Start laptop and then start tapping the F2 key and you should enter the bios

You will be able to access the Setup Bios Defaults there, reset, save and exit

If not F2, as mentioned, look at the screen when you first turn on and you will see the options there