Help needed to edit macros due to change in data range

Give this a try

Option Explicit

Sub test()
Dim myDate As Date, x As Double, temp
Dim Avbl As Long, Bkd As Long, DBkd As Long
Dim rng As Range, a, w, flg As Boolean
Dim i As Long, ii As Long, iii As Long
    With Sheets("Check Availability")
        myDate = .Range("D3").Value
        Set rng = .Range("B5", .Range("B" & Rows.Count).End(xlUp)).Resize(, 27)
        Avbl = .Range("J3").Interior.Color
        Bkd = .Range("M3").Interior.Color
        DBkd = .Range("Q3").Interior.Color
    End With
    With rng
        With .Offset(1, 2).Resize(.Rows.Count - 1, .Columns.Count - 2)
            .Interior.Color = Avbl
            .ClearComments
        End With
    End With
    If myDate = 0 Then GoTo Exit_Sub
    a = Sheets("View ; Make Reservation").Range("B3").CurrentRegion.Value
    With CreateObject("Scripting.Dictionary")
        .CompareMode = 1
        For i = 1 To UBound(a, 1)
        If a(i, 1) = "" Then Exit For
            If a(i, 1) = myDate Then
                If Not .exists(a(i, 2)) Then
                    ReDim w(1 To 3, 1 To 1)
                Else
                    w = .Item(a(i, 2))
                    ReDim Preserve w(1 To 3, 1 To UBound(w, 2) + 1)
                End If
                w(1, UBound(w, 2)) = Round(a(i, 3), 6)
                w(2, UBound(w, 2)) = Round(a(i, 4), 6)
                w(3, UBound(w, 2)) = a(i, 5)
                .Item(a(i, 2)) = w
            End If
        Next
        If .Count = 0 Then GoTo Exit_Sub
        Application.ScreenUpdating = False
        For i = 2 To rng.Rows.Count
            If .exists(rng.Cells(i, 1).Value) Then
                w = .Item(rng.Cells(i, 1).Value)
                For ii = 1 To UBound(w, 2)
                    For iii = 3 To rng.Columns.Count
                        x = Round(rng.Cells(1, iii).Value, 6)
                        If x = w(1, ii) Then
                            flg = True
                        ElseIf x = w(2, ii) Then
                            Exit For
                        End If
                        If flg Then
                            If rng.Cells(i, iii).Interior.Color = Avbl Then
                                With rng.Cells(i, iii)
                                    .Interior.Color = Bkd
                                    .ClearComments
                                    .AddComment w(3, ii)
                                    .Comment.Shape.TextFrame.AutoSize = True
                                End With
                        Else
                                With rng.Cells(i, iii)
                                    .Interior.Color = DBkd
                                    temp = .Comment.Text
                                    .Comment.Delete
                                    .AddComment temp & vbLf & w(3, ii)
                                    .Comment.Shape.TextFrame.AutoSize = True
                                End With
                            End If
                        End If
                    Next
                    flg = False
                Next
            End If
        Next
    End With
Exit_Sub:
    Application.ScreenUpdating = True
    Set rng = Nothing
End Sub

Replace the code in your Check Availability sheet to this

Private Sub Worksheet_Change(ByVal Target As Range)
    If Not Intersect(Range("d3"), Target) Is Nothing Then
        If Not IsDate(Range("d3")) Then Exit Sub
        Call test
    End If
End Sub