if you've checked your Settings and your backup account is no longer listed in Backup & Restore, and the option to input the account is grayed out, clear the partition cache on your phone. this will restore your backup account. this is not the same as clearing the cache in Storage under Settings. follow the directions here, Clear the Cache Partition - Droid Turbo 2, to clear the partition cache. the steps for marshmellow still work for nougat.