Inspired by shows like That Time I Got Reincarnated As A Slime and Tsukimichi: Moonlit Fantasy

A young dragon hatchling who recently became a dragon lord wants to unite the magical creatures and humans together after a purge of most of the dragon lords from 30 years ago by group of "heroes" caused the collapse of several human kingdoms Because of the sudden politicak power imbalance and for many magical creatures to go into hiding the party are all reincarnated individuals who have died and have been summoned to this world by the dragon king's newly appointed mage in order to assist him in something

Now heres where I get stuck at I don't know what the party needs to do to help the king, either it's the king win over allies or murder an attacking human army but nevertheless i need some ideas