I forgot my 4 digit code to erase all my content off my iPhone 6s Plus. Is there any way around this?

Erase your device from iCloud. Its simpler and much easier. No point fiddling with the device when you are unaware of the codes to allow access.

That's irrelevant. Is it asking you for a restrictions passcode to erase it from the settings? If so, you need to follow the instructions I've already provided. If not, then please be more specific. Post a screenshot of possible.

That sounds like a restrictions passcode. If you've forgotten that you'll need to either erase it from iCloud as Lawrence mentioned, or use recovery mode and iTunes.

https://support.apple.com/en-us/HT204306

You don't need a 4 digit passcode, unless you mean the screen unlock code. What you need is your Apple ID passcode.

You can also erase your content by logging in to https://icloud.com/Find using your Apple ID and passcode. Click on your phone and put it in Lost Mode, then Erase it.