Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
In most cases, you should be able to reinstall Office from your associated account at https://account.microsoft.com/services .
Which specific Office 2019 product is this? For example, is it Office Home & Business 2019? Or something else?
In case activation fails, see https://support.microsoft.com/en-us/windows/activation/activate-microsoft-perpetual-products-using-the-product-activation-portal .