These are the instructions for erasing data. Find the one that applies to your device. We need ALL Apple devices to have their data erased (it's fairly simple) to make sure we can use them. Email email@example.com with questions.
Before you sell or gift your Windows 10 device or Xbox One - Microsoft Support: https://support.microsoft.com/en-us/help/10547/microsoft-account-selling-gifting-windows-10-device-xbox-one
Windows 10 basics: how to reset your system - The Verge: https://www.theverge.com/21264104/windows-10-reset-os-reboot-troubleshoot-microsoft
Recovery options in Windows 10 - Microsoft Support: https://support.microsoft.com/en-us/help/12415#section2 and pick "Remove everything"
How to refresh, reset, or restore your PC - Microsoft Support: go to the "Reset PC" section - https://support.microsoft.com/en-us/help/17085/windows-8-restore-refresh-reset-pc
Instructions in progress, you will likely be able to find something if you look it up with a search engine. Email firstname.lastname@example.org if you need help with this and someone will get back to you soon.
What to do before you sell, give away, or trade in your Mac - Apple Support: https://support.apple.com/en-us/HT201065
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support: https://support.apple.com/en-us/HT201351
For other types of devices you can often look up "how to reset [device]" in a search engine. If that does not help email email@example.com.