Convert List into Ienumerable

HI
I am using LINQ for data connectivity and have made class which return me the result set  into presentation here is the syntax:-
public List<ClsDermaInvestigation> MthdisplayInvestigation()
        {
            List<ClsDermaInvestigation> lstinvst = new List<ClsDermaInvestigation>();
            ISingleResult<USP_Patient_Dermatology_InvestigationResult> investresult = objderma.USP_Patient_Dermatology_Investigation(PatientID, RepDate, Hb, TLC, F);
            foreach(USP_Patient_Dermatology_InvestigationResult rel in investresult)
            {
                
   &n ...