This is the procedure according to page 85 of the user guide from »ftp
://ftp.zyxel-tech.de/2.new_ ··· 3_v1.pdf
How to reset this device as factory default?
Upload the default file to IES1000 by ftp, web. Or upload the bin file by BOOTP/TFTP.
Please ftp into the DSLAM. Replace the init with the default rom file by put