If you can mount it some how, try...
$ mount/override=id dka100:
$ analyze/disk/repair/read dka100:
-Steve
SF:IP2
  On Mar 30, 2020, at 18:14, G. <gerry77 at
mail.com> wrote:
 
 ?On Mon, 30 Mar 2020 17:51:21 -0400, Supratim Sanyal wrote:
 
  What is the recommended way to recover from
"FILNOTCNTG" error? 
 
 Boot the system in some other way (cluster satellite, CD-ROM, etc.) and
 check that SYSBOOT.EXE is contiguous:
 
 $ DIR/FULL DKA100:[VMS$COMMON.SYSEXE]SYSBOOT.EXE;0
 
 The "File Attributes" line must show "Contiguous" and hopefully
"MoveFile
 disabled" too. If not, COPY/CONTIGUOUS it to a newer version of the same in
 the same directory and try the boot again.
 
 The other possibility is that the volume is damaged or does not contain a
 valid VMS file structure. In this case the FILNOTCNTG error is just an
 indication that VMB.EXE (in ROM) got very confused by your disk's contents.
 
 HTH, :)
 G.