Having issues with a if do else statement

I have been trying to make this work for a bit but have no idea how to

If is Event/target entity creature type undead

Do Execute Command /"effect give @e[distance=..5] minecraft:instant_healing 10 3 at x: x y: y z: z

Else Execute Command /"effect give @e[distance=..5] minecraft:instant_damage 10 3 x: x y: y z: z

I can't get it as an image so I just typed it out