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If you can not find any Office on your Mac, which does not match the information of pre-installed Office you got at the time of purchase.
I agree with JohnKorchok, it's best contact the seller to have a further confirm, check whether there is any additional instructions for installation or activation.
General, if you have a new purchase of Office, the first thing to do is redeem the product key to bind your Microsoft account to Office's license.
Go to www.office.com/setup, sign in with your Microsoft account, or create one if you don't have one. This account can be used to install or reinstall Office later, without a product key.
For more, you can refer to "Redeem a product key or activate Office".
Any updates, welcome to post back.
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