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If it was only an adult dragon then the DC is only 16, making it far more likely you'll succeed - after 1 turn most of your party will be unaffected:

1. Wait it out. Frightful Presence lasts for 1 minute max and makes you immune for the next 24 hours. Once you are frightened simply run and/or hide then re-engage. If all you do is long rest then go back and fight them, you will still be immune to Frightful Presence making the fight a lot simpler. For this reason dragons will usually hold off on using this feature until it looks like they are going down, it's a feature that turns fights around.
2. Break line of sight. There are numerous spells you can use to break line of sight, you can also do mundane things like dip around corners. This is a good time to cast buffs like Guidance so you can make that check faster, you can also use other buffs or items during this time. Another thing you can do is;
3. Do things that don't require attacks/ability checks. For spell casters this is super easy, they have tons of spells which require an enemy to make a check. This means they can operate without fear affecting them at all.

Keep in mind that although the dragon's DC19 is scary, on average with +0 Wisdom Saving it only lasts about 5-6 turns. Even a cantrip like guidance reduces that average length down to 1-2 turns. Ironically it's nowhere near as scary as it looks.

1. Wait it out. Frightful Presence lasts for 1 minute max and makes you immune for the next 24 hours. Once you are frightened simply run and/or hide then re-engage. If all you do is long rest then go back and fight them, you will still be immune to Frightful Presence making the fight a lot simpler. For this reason dragons will usually hold off on using this feature until it looks like they are going down, it's a feature that turns fights around.
2. Break line of sight. There are numerous spells you can use to break line of sight, you can also do mundane things like dip around corners. This is a good time to cast buffs so you can make that check faster, you can also use other buffs or items during this time. Another thing you can do is;
3. Do things that don't require attacks/ability checks. For spell casters this is super easy, they have tons of spells which require an enemy to make a check. This means they can operate without fear affecting them at all.

Keep in mind that although the dragon's DC19 is scary, on average with +0 Wisdom Saving it only lasts about 5-6 turns. Ironically it's nowhere near as scary as it looks.

There are a few classic ways to deal with dragon fear:

In my experience there are a few classic ways to deal with dragon fear: