Once you have multiple auctions in your account you can switch between them in a couple of ways:
Click on the dropdown arrow next to the auction name in the header and choose the event from the menu
Click on Auctions in the left hand menu, then choose All Auctions and click on the row for the event you want to see:
When you first sign into Auctria the system will open the next upcoming auction, unless there is an event that is dated less than two weeks in the past, in which case it will be chosen.
If you create a bookmark in your browser after signing into Auctria then it will be hardcoded to a specific event.
In future years you would need to create a new bookmark to link to the current auction.