Can you please let us know the make and model number of your laptop as the key or key combination can vary. Without this information, the best I can suggest is that you check your manual and follow the instructions there.
I had already scan my pdf manual and I wasn't able to find any solution for my problem. I also tried to examined the settings from my device manager, mouse property settings but I still could not find the solutions.
This took a bit of finding, but I hope that the information in the following link helps. This is for disabling the touchpad - to reenable it follow the instructions except at Step 5 you need to check the box instead of clearing it.