Trying to get the back cover off a Dell E770s. The service manual
says to use an 'opening jig' to pop the latches. So far, Google is
unhelpful - lots of monitors seem to use one ("Push the Opening jig
each groove along the top of the monitor till it makes a “ttak”
sound."), but I'm not finding anything about the jig itself.

Any info on where to get one, or how to make one, would be
appreciated.

George,
Just about any metal (long blade screwdriver) that fits the opening
and that's strong enough not to bend too easily should work. By
carefully examining the outside of the cabinet (look for irregular
pattern), you can sometimes make out where the fasteners are inside.
With the monitor face down on a cloth, and while pulling upward on on
the rear of the cabinet, pry back and forth until you hear the catch
release on one side. Shove something in the space between front and rear
so it doesn't re-latch, then do the same on the other side.

^ pry this way
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===== slot in cabinet
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v or pry this way

Ray