I am looking for a starter button for Atlas Copco, Portable compressor XAS30 Dd (has Deutz diesel engine). The button has 3 connections on the back and the button pushes a metal wash connecting presumably the 3 terminals.

Your particular model does not come up on the Atlas Copco website strangely however they do seem to use the below button across all of the smaller models if this looks correct? https://www.lsengineers.co.uk/push-button-atlas-copco-no-1089-9326-01.html