you need to download all 3 files  - follow the .txt instruction 

Introduction on how to create a USB Stick to restore Robotino OS / image (operating system)

Robotino has a SSD that stores the operating system.
A bootable USB stick is used to initially install the Robotino OS to a new SSD or
overwrite the OS on a SSD already in use.

*****Create a bootable USB-Stick*****

If you are using the USB-stick that shipped with Robotino you can skip to step number 4.
If you use a new USB follow Step1-3:
1) Download the Robotino custom image. (e.g. CoreCustom_20211029.iso)
2) Take a USB-Stick and format it (quick format will do)
3) Use UNetbootin (https://unetbootin.github.io/) to install this custom image to the USB stick.

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4) Download a Robotino4 image and it's md5 file. (With Firefox you need to right-click the file and choose save link.)
5) Check the integrity of the image using md5 (http://www.withopf.com/tools/md5/)
Run md5 -Check:imagefilename.fsa.md5.

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6) Copy the image files (.fsa,.f01,...) into the /images/ directory of your USB-stick.
e.g. robotino4-4.20.10.fsa and robotino4-4.20.10.f01
Note: if images folder is missing, copy to boot folder.

7) Attach monitor and keyboard to your Robotino.
8) Plug the USB stick into any of Robotino's USB port.
9) Please do not continue without plugging in Robotino to it's power supply.
10) Power on Robotino and hit the
F7 (for Robotino Professional with Core i5),
F11 (for Robotino Basic with Atom) as long as you can see the BIOS startup screen.

11) Select your USB stick from the list (not the UEFI entry).
12) Select Microcore from the list - this will start the automatic updater.
13) After booting into tinycore type restore.sh and press Enter to start the restore process.

furter reference https://www.openrobotino.org/