Convert data (a bit like a FOREACH?)

If you want the event names added, you're going to need to provide a complete event id / event name lookup table. This code does not add event names for that reason.

Sub simonp820()

Set ws1 = Sheets("query_result")
Set ws2 = Sheets.Add(After:=Sheets(Sheets.Count))
ws2.Name = "output " & Sheets.Count

ws1.[B1:E1].Copy ws2.[A1]
ws2.[E1].Value = "event codes"
uid = ""
r = 1

For Each c In ws1.Columns(2).SpecialCells(2, 1)
    If c.Value <> uid Then
        r = r + 1
        Set d = c.Resize(, 4)
        d.Copy ws2.Cells(r, 1)
        ws2.Cells(r, 5) = c.Offset(0, -1).Value
        uid = c.Value
    Else
        ws2.Cells(r, 5).Value = ws2.Cells(r, 5).Value & ", " & c.Offset(0, -1).Value
    End If
Next

ws2.Columns.AutoFit

End Sub

I'm more inclined to use Range.Find then Vlookup, if only because I'm more familiar with it. If you have a massive data set to search (like 100,000+ rows), then I've seen that Vlookup can be faster. Otherwise it doesn't really matter.

Please note I've changed the sub as well as added the Function. Also assumes event id's are in column A on "events" sheet. If not, adjust Columns(1) in the function.

Sub simonp820_2()

Set ws1 = Sheets("query_result")
Set ws2 = Sheets.Add(After:=Sheets(Sheets.Count))
ws2.Name = "output " & Sheets.Count

ws1.[B1:E1].Copy ws2.[A1]
ws2.[E1].Value = "event codes"
ws2.[F1].Value = "event names"
uid = ""
r = 1

For Each c In ws1.Columns(2).SpecialCells(2, 1)
    If c.Value <> uid Then
        r = r + 1
        Set d = c.Resize(, 4)
        d.Copy ws2.Cells(r, 1)
        ws2.Cells(r, 5) = c.Offset(0, -1).Value
        uid = c.Value
        ws2.Cells(r, 6).Value = event_name(c.Offset(0, -1).Value, "")
    Else
        ws2.Cells(r, 5).Value = ws2.Cells(r, 5).Value & ", " & c.Offset(0, -1).Value
        ws2.Cells(r, 6).Value = ws2.Cells(r, 6).Value & event_name(c.Offset(0, -1).Value, ", ")
    End If
    
Next

ws2.Columns.AutoFit

End Sub

Function event_name(eid As String, spacer As String) As String
    Set c = Sheets("events").Columns(1).Find(eid)
    If Not c Is Nothing Then event_name = spacer & c.Offset(0, 1).Value
End Function