Good luck with that!
https://www.germany.info/us-en/service/09-Taxes/vat-refund/906296
You need to visit customs on the way out,
present the store receipt,
the goods, your passport and your tickets, in addition to the tax-free export form (which hopefully you were able to get from the store), in order to get that form stamped so you can mail it back to the store you made the purchase at, in order to request a refund check in the mail.
Oh, and since you need to present the purchased goods directly to customs, you'd better hope they're eligible to be brought in carry-on, and you have carry-on luggage space, because you won't have your checked luggage at that point. How much experience do you have taking tools through airport security. I have too much, and it's always been a **** show, though at least Germany is much better about it than the TSA. But the language barrier isn't going to help. It may not be much of a problem in at customs, but it's very likely to be a problem when you're requesting the requisite form at the store.
And after all that, the store may simply refuse to send you a refund. And you have no recourse.