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Can't help with who to do it, but avoid those vape shops that do screen repairs unless you know 100% that a) they've repaired that particular model before and they know what they're doing and b) they're going to use a genuine Apple screen.
For a), if they sit there and follow a Youtube repair video (likely) there's a good chance they'll break something. For b), if they use a non-genuine screen the colour resolution will be wrong and it won't be as responsive as an original. I found both of those out first-hand.
Edit: back glass is not the screen, right? The above may not be relevant then.
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Can recommend. I-smash:
iPhone XS back glass repair.
My wife has broken the glass on hers and wants to get it replaced. Apple want crazy money to do this. Which other companies are worth using - ideally a mail in service.