want to transfer data from iphone 7 to iphone 6

Check here:https://support.apple.com/en-us/HT201269 not all data will be transfered as the 6 does not support ios 13

You can sign into your iCloud account on the 6 and sync your contacts, etc. to the 6, but you will not be able to restore a backup of the 7 to the 6 assuming the 7 was running iOS 13.

Then they may have been synced to a different email account. Add that account to the 6 and turn on contact syncing for it.