As mentioned in the comments, your code is vulnerable to SQL injections, recommend you use parameters.
As for your problem, I think you need to adjust the code just slightly:
Else
Dim aantal As Integer = txtHerhaling.Text
Dim gebruik As Integer = 0
Dim startDate As Date = Date.Today
Dim endDate As Date = dtpEndDate.Text
Dim currDate As Date = startDate
Do While (currDate < endDate AndAlso gebruik < aantal)
SQL = String.Format("INSERT INTO tblManual (StartDate, EndDate, UniqueID) VALUES (#{0}#, #{1}#, '{2}')", currDate, endDate, id)
scmdRecurrence.CommandText = SQL
Valueee += 1
scmdRecurrence.ExecuteNonQuery()
currDate = currDate.AddDays(7)
gebruik += 1
Loop
MsgBox(Valueee.ToString & " records toegevoegd")
End If