Reformat and partition your startup disk

Before restoring from your Time Machine backup, you must first partition and reformat your startup disk. Partitioning your startup disk permanently deletes all of the data stored on it.

To begin, select Disk Utility from the macOS Utilities window in macOS Recovery, then select your startup disk. Be sure you are selecting the entire disk (not the volume name indented beneath it), by selecting View > Show All Devices, then select the disk and choose Partition. If prompted to add a volume to the container or partition the disk, choose Partition.

Disk Utility will present a pane where you can configure your partition. Under Format, choose APFS if you are restoring a Time Machine backup of macOS Mojave or later. Otherwise, choose Mac OS Extended (Journaled). Then choose Apply.

When done, quit Disk Utility to return to the macOS Utilities window.