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Hi @realpp,
That is your phones model number and it cannot be changed. I hope this answers your question. 
@realpp do you want to change the name your phone is visible under when connecting via Bluetooth? if that's what you mean, go to Settings > Bluetooth, turn it on, then tap on the three dots in the top right corner and select Rename this device.
also, what file names do you want to change?
Hi @realpp,
That is your phones model number and it cannot be changed. I hope this answers your question. 
1 Question
Before reset my phone name is xperia xz1 ?
why not to default name?
@realpp, I'm not quite sure I understand your question. Your device is still called Xperia XZ1 but its model number is G8342. Resetting the device will not change this.