I describe this process in my last training about LInkedIn. The basis is, going on Google and performing a "Google Search Operator" method to reach specific prospects. For example, you wanted to reach marketing managers, then you would type in the following (in case you can't see it in the image):

site: LinkedIn "mareketing manager" "present (2 months)"

Note: You can type in any position and any timeline you like to know using this method. You are not confined to only the example