Instructions for the Reinstall directory are here: https://help.roonlabs.com/portal/en/kb/articles/roonos-reinstall-directory-instructions#Using_the_Reinstall_Directory
You will need to use this file: roonos-production.bin
(above download link edited to be the correct one for RoonOS)
Short version is:
- Download the file linked above to your computer
- Mount the Data folder from your RoonOS device on your computer and navigate to the Reinstall folder
- Copy the downloaded file to the Reinstall folder
- Hit the reinstall button on the admin page