sql problem, how to add date time picker

Firstly, your code is at risk of SQL Injection[^] - never concatenate user input into sql statements like this.

Use parameterised queries[^] instead.

One of the advantages of using parameters is also not having to worry about single quote marks on date and text fields.

Your code could be changed as follows

Dim sql As String = "SELECT remittance_no, remit_date, messenger, item, item_value, rate.product, rate.product_value "
sql += "FROM remittance INNER JOIN rate ON rate.product=remittance.item "
sql += "where rate.ratecode = @RateCode And remittance.messenger = @Messenger "
sql += "and remit_date between @Date1 and @Date2 "
sql += "order by remit_date asc"

Then assuming you have something like

Dim command As SqlCommand = New SqlCommand()

and the associated connection etc (or just substitute your variable name for command in the code below.

command.Parameters.AddWithValue("@RateCode", txtRateCode.Text)
command.Parameters.AddWithValue("@Messenger", txtRateCode.Text)

command.Parameters.AddWithValue("@Date1", DateTimePicker1.Value)
command.Parameters.AddWithValue("@Date2", DateTimePicker2.Value)

Note that with DateTimePicker controls you can avoid the time element by using

DateTimePicker1.Value.Date