Let’s say you have an Android phone in which you already have a Google account, possibly your main Google account. If the data from the new account (e.g. Contacts), must not get mixed up with data in your current account (your existing Contacts), the following should help:
Keep the data/wifi connection turned on throughout. We will control this setting using the Airplane mode.
- Turn off Sync in Settings -> Users and accounts - the general one that applies to all accounts.
- Add a Google account (you need an internet connection to do this)
- Turn on Airplane mode (now internet connection is off)
- Turn on Sync in Settings -> Users and accounts (only then will the sync controls of apps of the new account would be available for you to turn on/off).
- Turn off sync for most apps - you may want to turn it on only for a few apps e.g. gmail, in case you need to know when you get email for the account being added.
- Note that Airplane is still turned on so since we don’t want data to get downloaded in the few seconds between creating the account and disabling sync.
- Google Drive: if sync is turned on, all your files will get downloaded.
- Turn off airplane mode.
- Verify if the apps of the new account, e.g. gmail, which have sync turned on, work as expected.
