I've taken an Autometer apart and also a 'Defi'
, but 'FAILED' when taking apart a ProSport (not worred
as alot cheaper then the Defi would of been if I knackered that one).
Defi and Autometer just need the rear crimping of the front bezel lifting with a small blade until you can work the back cover off. Sometimes there is also a couple of small screws holding the back cover on.
Once that's off you may need to remove the needle to get the dial face off and access to the circuit board.
Best thing to get the need off is the back of a tea spoon slide underneath.