iphone 6 s how do i gain access to the serial number please

See this support article:--> Find the serial number or IMEI on your iPhone, iPad, or iPod touch - Apple Support

Since, instead of the serial number, you can use the IMEI number, depending on your iPhone model, pull out the SIM tray from your iPhone and the IMEI/MEID should be engraved there.

Regards

Giulio

There are a lot of ways to get your serial number of your phone, please refer to the below article.

https://support.apple.com/en-us/HT204073

If you can turn it on

Settings, General, About

Glad we could help you :)

Giulio