As already referred to, it would make a big difference if you can clarify a significant contradiction. Apparently this tablet is not actually 'brand new' (first time used) but rather pre-owned but 'new' for you (just purchased by you from a previous owner). If it was indeed brand new, there would be no Google user account previously set up on it. A new device will prompt the user to enter one. Or is it a matter of what B. Diddy inquired, you just mistakenly entered an incorrect Google user account and want to change it?
You do need to use the original Google account to log in, then remove that account and enter the Google account info you do want. Keep in mind that the Google account that the tablet gets assigned to does not necessarily have to the same as the Google account you use to set up the email app or whatever. There is a difference between the Google account the device is linked with and the user account that get used for the various apps that link up to online Google services -- when doing a Factory Reset, this only does one thing, it wipes the user data partition. It does not affect the installed Android operating system. (The internal storage of any Android device is divided into several partitions. Most are dedicated to the operating system and are protected and restricted. One partition, the largest one, is set to be the user's data partition. You, the user, have complete control and access to anything on that user data partition but little to no access to any of those system-level partitions.)
If you don't have access to that original Google account, than it becomes a bigger problem. Again, a Factory Reset only wipes the user data, and the device Google account is tied to the installed operating system so all that does is clear out whatever user account data was previously saved. Without the original login info, you need to re-flash a stock ROM. Flashing the firmware replaces the installed OS with a clean, new one. Depending on the tablet model, obtaining a valid stock ROM could be an issue -- i.e. Samsung ROMs are pretty prevalent and obtainable from several online sources while ROMs for minor brands/knockoffs are scarce to non-existent.
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