If your firmware is corrupted or you have installed third-party software (like Tenda firmware), you cannot easily revert to the original PTCL version unless you have an ISO backup. In such cases, PTCL recommends visiting a service center for professional re-installation.
Ask for the latest firmware for the F-ST 4315. They can push it remotely or provide a download link. sagemcom f-st 4315 ptcl firmware
Official firmware for PTCL-branded Sagemcom devices is rarely hosted on public Sagemcom sites. You should check these primary sources: PTCL Official Support : Visit the PTCL Drivers and Software page to see if the specific F@st 4315 update is listed. Sagemcom Support Sagemcom Product Selection tool If your firmware is corrupted or you have
Sagemcom offers firmware but often requires a login: https://www.sagemcom.com/en/support sagemcom f-st 4315 ptcl firmware