First of all, I need you to confirm that it is a ZyXEL VMG1312-B10A.
Assuming that is the case, you will need to obtain the password to the supervisor account. Establish a telnet connection to the device and, once logged in via the admin account, issue a dumpmdm command. That command will output many lines (something in excess of 6500!) and somewhere around line number 140 - 150 will be seen <AdminUserName>supervisor</AdminUserName> followed, on the next line, by <AdminPassword>xxxxxxxx</AdminPassword>. Make a note of the eight hexadecimal digits (where I have shown xxxxxxxx), for that is your supervisor password.
Login to the supervisor account and go to the Maintenance > Configuration page. Select the ROM-D tab and then left-click on the Clean button. The deed is now done.
Thanks to you both for your help. I managed to get this done and the modem cleaned last and all is well,one the reasons I wanted this was for line stats, the line used to sync higher so not sure why its gone down, wondering how hard it would be to get BT to do a line reset
VDSL Training Status: Showtime
Mode: VDSL2 Annex B
VDSL Profile: Profile 17a
G.Vector: Disable
Traffic Type: PTM Mode
Link Uptime: 0 day: 7 hours: 31 minutes
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VDSL Port Details Upstream Downstream
Line Rate: 20.202 Mbps 74.620 Mbps
Actual Net Data Rate: 20.000 Mbps 74.507 Mbps
Trellis Coding: ON ON
SNR Margin: 6.9 dB 6.3 dB
Actual Delay: 0 ms 0 ms
Transmit Power: - 8.4 dBm - 8.4 dBm
Receive Power: -12.6 dBm 6.0 dBm
Actual INP: 0.0 symbols 0.0 symbols
Total Attenuation: 0.0 dB 9.2 dB
Attainable Net Data Rate: 24.194 Mbps 74.511 Mbps
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VDSL Band Status U0 U1 U2 U3 U4 D1 D2 D3
Line Attenuation(dB): 0.1 9.1 14.0 N/A N/A 4.9 11.0 19.2
Signal Attenuation(dB): 0.1 9.0 14.1 N/A N/A 4.8 10.9 19.1
SNR Margin(dB): 7.4 6.8 6.9 N/A N/A 6.4 6.3 6.2
TX Power(dBm): -12.8 -51.0 -10.5 N/A N/A 10.3 7.4 7.5