That is definitely going to be a challenge, the Greeks were far out numbered by Pārsa and were disunited it seems. Their most powerful land military (the Laconians) was very small compared to the Pārsan army and was celebrating a festival during the Battle of Thermopylae, if you're looking for a POD to change it, change the date of the Battle of Thermopylae so the full army of Laconia was there, or have the Greeks know when to give up, as is only a few Greeks escaped that battle.*
If they survived 480 BC, then they still have to contend with later invasions, but it might be far more difficult for Pārsa to take control of the region as completely as they did IOTL.
* POD for DBWI: the Persians never find the goat path and instead both complete armies meet face to face at Thermopylae, the superior numbers of the Persians allow them to kick Greek ass, and Greeks were always a little too badass for their own good so they didn't retreat until it was too late, the navy at the Battle of Artemisium didn't retreat until the battle of Thermopylae was lost, but by then they were pretty much done for so Salamis went poorly