Looks like you want to find all rules with a given name and check condition for some /all of such rules. Use Where
to filter out rules you want and Any
or All
depending on your needs to check condition... With current sample Any
should be enough:
var fileExists = FileParms
.Where(r => r.Name == ParmNames.FileName) // find all "File names"
.Any(r =>File.Exists(r.ValueEnvironment) // check if any of the files exist