Hello Shuesawhau82
You probably mean the connection at 08:39 from Lucerne, with a change at Arth-Goldau.
If you miss the connection because you were dallying around, the ticket is no longer valid because it is only valid on that EC while the seat reservation is part of the ticket. You need a new ticket or change it at the counter with a new reservation for the next EC. In Italy, everyone needs a seat reservation for the EC.
Kind regards,
Roland