Hi there, I have kept GSD's for more years than I care to remember, I love when they go through the floppy ear phase you never know what they will look like from day to day, 5 months is still quite young although some dogs ears stand up much earlier, you don't need to do anything to help them, they will stand up when they are ready, usually all GSD's ears are up by 6 months, I have a 14 month old and didn't think hers would ever stand, but one morning, hey presto! she was 5 and a half months old, sometimes when the dog gets tired you may find that 1 or both will flop again but bit by bit they will get stronger.