Hi , I contacted Nokia chat service and I was shocked to know that there is no replacement policy for Nokia 8 even there are manufacturing issues with the phone.
In the UK at least it is very complicated when it comes to refunds, replacements or repairs as it is all about time frames and in a case like yours you would have to prove there was a manufacturing issue at the time of purchase. Also your contract of sale is with the retailer and not Nokia so it would have nothing to do with them.
Again this is for the UK only and then i have overly simplified it, i have no idea about elsewhere.
What kind of manufacturing issues do you have with your device that would require a replacement? You can check our warranty details here:
First do a factory reset, could be that fixes the issue, and they will almost certainly ask you if you did a reset first.
If not resolved ,check with the store you bought the phone from and try to reproduce the issue there, if it's clear that there's something wrong with the phone then it should be covered by warranty. I haven't had the issue that you're describing.
Otherwise e-mail support here, IME answers you get this are more reliable than the chat support : https://www.nokia.com/en_in/phones/support#contact-us