Office 365 Keys - How to find/uncover

I have just won two windows 8.1 tablets from work.

Each is supposed to include office 365 for 1 year from activation.
I am considering selling the tablets, as I already own three windows 10 tablets!

I simply need to check the status of the office 365 (1 year) keys, - WITHOUT activating or registering them.
Please help.

I have not connected the tablets to the internet - I want to back them up first.

Is there any way to uncover the key for the free 1 year sub, through command promt or something?

Is there any way to get they keys - so I can then check theri status via microsoft chat?

Thanks in advance.