Reset devide remotely - please read!

A

AC Question

My device's screen has stopped responding to my touch. As a result, I got a new device and transferred the sim card. I will be returning the phone to the (online) seller. I do not want anyone to see the stuff on my phone, which is pattern-protected but not encrypted. I tried googling "find your phone" and requested an erase, but my phone is not online. I do want to make sure that when someone plugs the phone into a pc, they wont be able to see all my stuff. But since I dont have the computer-plug-in cord (whatever its called), I'd prefer to do the reset without having to borrow one. How would I go about this. Thanks.

PS Galaxy tab 4