There could be any number of reasons why you might need or want to perform a factory reset on your Samsung Galaxy S6, and whatever those reasons are the process of how to complete a factory reset is something you should be familiar with. It isn't an overly complicated process, and there are a couple ways to go through with it so we'll be going over both methods. One involves navigating to the settings menu and accessing the function that was built into the software, while the other involves utilizing hardware buttons to perform the task. Each method ends up with the same result, which is a device that has been wiped clean of all its data and all the settings back to factory configurations just like when the device was brand new and powered on for the first time.
First things first, before doing a factory reset on your device, you likely took notice that the process will wipe all of your data. Assuming you have important stuff on the device you want to keep, you'll want to make a backup of all your data before starting this process. You can initiate a backup of all your important data from the same place where you access the factory reset method. Simply navigate to settings, scroll down to the backup and reset menu, then once inside tap on the "backup account" option and proceed through the prompts. Once this is done you can move forward with the factory reset.
To reset your Galaxy S6 from the settings menu, head back into settings, scroll to the backup and reset menu, except this time instead of tapping on backup account you'll hit the option for factory data reset. Once you tap this option it will take you forward to the next screen which lists off all of the data that gets erased, this also serves as one final confirmation that all your data will be wiped and the device will return back to a factory standard. Once the reset starts, your Galaxy S6 should begin to reboot and spend the next minute or so performing the wipe. After the factory data reset is finished, begin the setup process for the phone again and perform the restore of all your data from whatever location you had it backed up to.
If for some reason you need to perform a factory data reset but you aren't able to get into the settings menu or power on the phone, the Galaxy S6 like all android devices has a built-in method for performing the factory reset via the hardware buttons. If the phone isn't already powered off, power it down so you can complete the process. Next, you will need to simultaneously press and hold the power button, the volume up button, and the home button. After a few seconds you should see the Recovery mode screen come up on the Galaxy S6 display, with a handful of listed options of things you can do from this menu.
You use the volume keys to navigate up or down and highlight the option you want, so use the volume down button to highlight factory data reset, then press the power button to select and confirm you want to complete it. After this you'll be taken to another screen which asks you to confirm you want to go through with the wipe. As with before, use the volume down button to highlight Yes and then hit the power button to select it. After hitting yes the factory data reset will begin, and once it has finished you'll be taken back the beginning screen of Recovery mode. Use the volume up button to highlight reboot system now, then use the power button to select it. The device might take a few minutes to reboot but once it's done you can restore all your data from wherever it's backed up. Note that this process will be the same for the Samsung Galaxy S6 Edge, so whichever model of the Galaxy S6 you have it doesn't matter.