Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
What can be done depends on how you initially got Office 2019. If it was preinstalled by the computer manufacturer, you won't be able to transfer it to a new PC. The install dies with the old PC.
On the other hand, if Office is associated with a Microsoft account, install it on the new PC. Phone activation may be required. See https://support.microsoft.com/en-us/office/-telephone-activation-is-no-longer-supported-for-your-product-error-when-activating-office-9b016cd2-0811-4cb3-b896-5a6a13177713 (even if you don't see the error message mentioned in the article).