You can't change the VOR/DME switch to AUTO when the HSI Mode Selector, on the EFIS panel, is set to either VOR or ILS (FULL or EXP). Set the HSI Mode Selector switch to MAP or PLAN, and  then you can then change between AUTO and MAN.

Note. Setting the HSI Mode Selector back to VOR or ILS, and the VOR/DME switch will revert to MAN.

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