Note that removing the account will also remove all messages from your phone, but your data will still be stored safely on the mail server. You will not lose any data by removing a Nexus account from your device.
1. To remove an existing Nexus mail account from your device before adding your migrated 365 mailbox, go to the Settings menu of your device and find a submenu called Accounts (may be titled “Cloud and Accounts”).
2. Tap Accounts. You’ll be presented with a list of all accounts configured for various apps on your smartphone. Look for an option that says Exchange or Microsoft Exchange – this will differ based on the app you’ve been using for your email.
3. You should then see a list of all the Microsoft Exchange Mailboxes that are configured on your device. If you have several and neet to choose from a list, tap the one you wish to remove. You’ll then see something similar to the following screenshot – tap the 3 dots in the corner and a menu will appear
4. Tap remove account to remove the account from your device.
The account is now removed from your phone and you can proceed to add your migrated Nexus 365 mailbox to the device.