If Column A contains one of several strings then change column Bs string

I am fairly new to macros in excel however I have done programming before. My biggest problem is figuring out the syntax for everything. So wondering if you guys could give me a hand.

What I need is to check to see if a cell in a column matches one of several different strings. If it does then I need to change another cell in the same row but different column to say DELETE. If it does not contain that string then I simple delete it So far I have this

Sub Loop_WIP()
    Dim First As Long
    Dim Last As Long
    Dim Lrow As Long


        First = .UsedRange.Cells(1).Row
        Last = .UsedRange.Rows(.UsedRange.Rows.Count).Row

        For Lrow = Last To First Step -1

            With .Cells(Lrow, "A")

                If Not IsError(.Value) Then

                    If .Value = "ItemA" or "ItemB" or "ItemC" Then

                        Change Value of Column B same Row
                    Else
                        .EntireRow.Delete

                End If

            End With

        Next Lrow

    End With

End Sub

Alternatively I could delete all of the un needed rows then go back with another macro to change all of row B to say DELETED. I still face the problem of not knowing how to format a cell change.