Tcl tv u55c7006 : how to backup my firmware and how to flash another tv with the backup ? using MKT Flash tool

[Ntsuab]

Hello,
I have two same TV. One is ok. The other is frozen with TCL logo. Updating with file Update.pkg looks running (after pushing 30sec to Home button) but message « Do not power off » remains for hours: flashing is blocked. Reading usb is stopped. At start the tv still frozen with logo.
My question: how to force flashing with tool like MKT Flash Tool ? And with which binaries ? Please help. Thank a lot.