how to modify a dynamic query?

ALTER PROCEDURE [dbo].[svg_monthlyvolumebyisobydatePro]
@isonum int,
@sdate varchar(25),
@edate varchar(25),
@view varchar(10)
 
AS
 
 
declare @sqlstm as varchar(8000)
declare @filter as varchar(10)
 
if @view='View All'
 begin
	set @view=''
 end	
 
set @sqlstm='SELECT '+
            @view+
           ' dbo.Locate.mid,
             dbo.address.corpname,
             dbo.Locate.dba,
             sum(BatchHeader.VisaMasterVolume) as netvolume,
             sum(BatchHeader.VisaMasterTransCount) as itemscount,
             CASE WHEN '+ @isonum + ' = ' + '9927' + 
                 ' THEN  dbo.Referral.ReferralName 
                   ELSE ' +  ''N/A''
             END AS refName
             FROM dbo.BatchHeader with(index(IX_BatchHeader),nolock) 
             INNER JOIN dbo.Locate with(index(PK_Locate),nolock) 
               ON dbo.BatchHeader.MerchIntID = dbo.Locate.intmid 
            INNER JOIN dbo.MerSum (NOLOCK) 
              ON dbo.Locate.intmid = dbo.MerSum.Intmid 
            INNER JOIN dbo.address with(index(PK_Address),nolock) 
              ON dbo.BatchHeader.MerchIntID =  dbo.address.intmid
            LEFT OUTER JOIN Referral (nolock) on 
                                        mersum.refid=Referral.refid 
            WHERE  (mersum.isonum='+convert(varchar(10),@isonum)+
            ' or mersum.Subisonum='+convert(varchar(10),@isonum)+
            ' or mersum.Subisonum in (select isonum from iso where  
                    referralpartner='+convert(varchar(10),@isonum)+'))
              and dbo.batchheader.datecreated >= 
                                  convert(smalldatetime,'''+@sdate+''') 
              and dbo.batchheader.datecreated <= 
                                 convert(smalldatetime,'''+@edate+''')
              and mersum.alternativeisonum is null
            group by   dbo.Locate.mid, dbo.Locate.dba, dbo.address.corpname, refName
            order by netvolume desc'
 
exec (@sqlstm)