Are you really asking here how you can continue to use a 365 license, although you are no longer entitled to use it?

Your Office 365 license is paid for by your previous employer. It is most likely an enterprise plan, and you can only use Office when you are logged on with a company account. If you don't work for that company any more, then you don't have a company account and you are not entitled to use that license.

You could stay off-line forever and continue to use the software (illegally). But as soon as you go online, like right now, reading this post, your PC will check for updates and will remove your Office license.

Office is not free and it is not cheap. Someone has to pay for it. Your employer did while you worked for them. Now you no longer do and you are no longer entitled to software that they pay for.

If that concept does not suit you, you may want to take a beginner class in ethics.