"Partner Guardian" is Home Depot's terminology to denote admin users within Supplier Hub. If additional applications or other general help is needed in Supplier Hub, your Partner Guardian should be able to provide access or help be a resource.
To see who your Partner Guardians are, follow these steps after you have logged into Supplier Hub.
Once in Supplier Hub, in the top navigation towards the right of the page, click "Account".
You will be redirected to a page that has your information listed.
This is also a good opportunity to make sure your information is up to date, particularly email. Home Depot uses the email listed here to provide important updates.
Below this, is a section labeled "Company Information". The names listed there will be contacts available to you with a Partner Guardian designation. These contacts can provide access to any additional applications needed within Supplier Hub.