Start by going to the BP_MasterWeapon blueprint and create a new variable then copy the video below.

Then tick the Instance Editable option.

Next create a new custom event called Melee Sound then copy the images below.

Then go to the BP_MasterMeleeWeapon and then to the Give Damage Once function, in that function are 3 Multicast Spawn Hit Emitter nodes with a Melee input, make sure that on all 3 of these nodes the Melee input is ticked on.

To learn how to use the new feature check out the feature guide linked below.