Shut down the computer while leaving the USB stick plugged in.
Plug in the other Tails USB stick that you want to install from.
Switch on the computer and immediately press-and-hold the Option key (Alt key) until a list of possible startup disks appears.
[[!img install/inc/screenshots/mac_option_key.png class="mac mac-clone" link="no" alt="'Option' or 'alt' key in the bottom left of Mac keyboard"]]
Choose the USB stick and press Enter. The USB stick appears as an external hard disk and might be labeled EFI Boot or Windows like in the following screenshot:
[[!img install/inc/screenshots/mac_startup_usb.png class="mac mac-clone" link="no" alt="Screen with the logo of an internal hard disk labeled 'Macintosh HD' and an external hard disk labelled 'Windows' (selected)"]]
If the USB stick does not appear in the list of possible startup disks:
If the computer starts on Tails, the Boot Loader Menu appears and Tails starts automatically after 4 seconds.
[[!img install/inc/screenshots/boot_loader_menu.png link="no" alt="Black screen with Tails artwork. Boot Loader Menu with two options 'Tails' and 'Tails (Troubleshooting Mode)'."]]
If your computer displays the Boot Loader Menu but then fails to start on the USB stick, it might currently be impossible to start Tails on your Mac model.
Please [[!toggle id="report-toggle" text="report the problem to our help desk"]].