Bit of an odd one, this.
I have a PC currently running Office 365 off a work account.
I have now left said employer and will, rather sadly, need to purchase my own Office 365 licence.
This is fine, but I think I need to find a way of logging out of my work account before logging in with another account that I can ourchase the licence with (does that make sence?)
The problem being that to manage my account I need to log in to it, and I no longer have the password. I’m stuck in a sort of not logged in or logged out limbo.
Help!!!

Try removing any saved office passwords in credential manager

Open Excel, go to File, Office Account, Switch Account then Add new account. You shouldn’t have to log out of your work account, the 365 admin should be able to disconnect you from the admin portal if it comes to that.

You’ll need full access to the new, personal account you’ll be using to manage the O365 subscription. You can access/manage/password reset this in a browser https://www.office.com/. That’s also where you can install the license if you bought from a third-party. Once that’s all good you’ll just need to login to that account from inside Office apps.

Not sure if your work also used Onedrive and whether you have any personal documents that were synced to your work Onedrive but worth figuring out and pulling them at the next opportunity.

Surely your old work account is, well, your old work account, and you shouldn’t be able to access it if you’ve left?

Windows 10 I assume with local apps? If so I think you need to go to settings > email and app accounts and delete the old account.

You might have to re-install Office anyway if moving from a business one using Office 365 ProPlus to an Office 356 home/personal edition.  Similar to this process;-

https://support.office.com/en-gb/article/migrate-from-office-365-proplus-to-office-365-personal-for-windows-10-692597ab-711e-459d-a916-663f5b8bdc30