If you want to develop this integration, please start from this doc -
so i need to develop a plugin first?
You are asking your question in the Developer Forum and therefore we might have assumed that you were asking because you wanted to develop a plugin.
Milestone Support will not always know if there is an integration already. Doing a search in marketplace came up empty: https://www.milestonesys.com/community/marketplace/start-exploring/?page=results&q=elid
There are integrations that are not announced in Marketplace, so I suggest you also ask the Access Control vendor. (I understand you are not the Access Control vendor.)