What is wrong in this query

I have a list AllIDs.
List AllIDs = new List();
I want to to substring operation on a member field AddressId based on a character "_".

I am using below LINQ query but getting compilation error:

AllIDs= AllIDs.Where(s => s.AddressId.Length >= s.AddressId.IndexOf("_")).Select(s => s.AddressId.Substring(s.AddressId.IndexOf("_"))).ToList();

Error:

Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.List'

I have a list AllIDs.
List AllIDs = new List();
I want to to substring operation on a member field AddressId based on a character "_".

I am using below LINQ query but getting compilation error:

AllIDs= AllIDs.Where(s => s.AddressId.Length >= s.AddressId.IndexOf("_")).Select(s => s.AddressId.Substring(s.AddressId.IndexOf("_"))).ToList();

Error:

Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.List'