How can I obtain the partyId when updating inventory?

I want to update inventory using submitInventoryUpdate(https://developer-docs.amazon.com/sp-api/docs/vendor-direct-fulfillment-inventory-api-v1-reference#partyidentification). How can I get the partyId in my vendor account?
<img width="1168" alt="image" src="https://github.com/clousale/amazon-sp-api-javascript/assets/80157042/769b5d9c-430f-47df-a974-e05a6ff61363">
