How to assign values to multi look up column

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SharePoint2013

I have a list which have a column which is lookupmulti type. Ihave to set values to the column.
Parent List

Employee ID Title
123 1
456 2
789 3

Child List (Which has the look up column)

EmpID Title
123;789 1

I have to update the child list's "EmpID" column with a list of string which is coming in request
the list contains two string values - 123,456
list<string> lst=new list<string>();
lst.add("123");
lst.add("456");

I have to update the information in the child list's "EmpID" column. How can I do this? Please suggest. A code snippet will be helpful.