I'm trying to add a ranged attack to the Sun Blade magic item, but can't figure out how to make it appear on the attacks section on the action page of a character sheet. I don't know if this can be done which is why I'm asking.

I've added this to the item's description field: "As an action, you can focus the Sun Blade’s light to strike a distant foe. Make a Ranged Weapon Attack against a target within 120 feet. On a hit the target takes 3d8+ your dexterity modifier in radiant damage. The sword cannot produce a blade nor use this feature again until the end of your next turn."

Then as a modifier I added: Modifier type - Ranged Weapon Attack / Modifier subtype - radiant / Ability score - DEX / Dice count - 3 / Die type - d8 / Details - same as the description above.

Thanks for any and all help.

You can't add actions to magic items right now. You either have to use a custom action or a feat to represent it.

Ah, shame. I was worried that might be the case, but with my relative inexperience with the homebrew functions on here I figured I may have just been going about it wrong.

Anyway thanks for the help, I'll find a workaround. 

The workaround is to add the attack to a feat.