Quickest way to DLC

I bought the new DLC after not playing elden ring for at least a year. When I got back on I realised I must have started NG+ when I last played and never continued.

Then I found out I can’t just start the DLC whenever I need to beat radahn and Mohg.

What’s the quickest way to beat these guys and start the dlc? I’ve played a lot of souls but I can’t remember anything about this game.

Thanks.