At the “Select a Backup Source” screen, choose your Time machine backup drive.

At the “macOS Utilities” screen, choose “Restore From Time Machine Backup” and then click Continue.

Reboot the Mac and hold down Command+R keys together to boot into Recovery Mode.

Connect the Time Machine volume to the Mac.

How to Downgrade from macOS Sierra with Time Machine If you skip that, you’ll lose the interim data. I personally get around this by creating a folder on the Time Machine volume and manually dragging and dropping important new documents into it, then just copy them back over to the restored Mac, but some users rely on iCloud Drive, DropBox, or other services. * Remember, a side effect of rolling back with Time Machine is that any interim data will be missing unless you manually back up the files yourself before beginning the process (for example, if you restored from January 1 but it’s now January 15, you would lose files created or modified between those two dates unless you manually back them up before the restore).

A manual backup (separate from Time Machine) of any interim documents or data created between the time of the Time Machine backup and now*.

Time Machine backup made prior to updating to macOS Sierra (either with Mac OS X El Capitan, Mavericks, Yosemite, or otherwise).

Requirements to downgrade from macOS Sierra to prior Mac OS X

The ability to prevent data loss, or roll back problematic software updates or OS upgrades is invaluable. This obviously requires a functioning Time Machine backup to work, one of of many reasons why setting up Time Machine on a sufficiently large external drive is one of the most important maintenance routines you can have on a Mac.

Upgrade el capitan to sierra