This is the first homebrew race I've made, and I'm making a racial trait that will do an unarmed strike doing 1d6 damage + your Strength modifier instead of bludgeoning damage, but I don't really know how-

You can’t modify the existing unarmed strike, but you can add an Action to represent your improved unarmed strike. Make it a “Weapon” action and set the parameters you want:

• Attack Range: Melee
• Ability Score: Strength
• Die Count: 1
• Die Type: d6
• Damage Type: [Whatever]
• Weapon Type: Natural
• Activation Type: Action
• Display as Attack: Yes