Minecraft Windows 10: Is there a way to enchant armor a player is wearing?

Just an idea:

First clear the player of his chestplate
(Clear Command)

Then Clone/Setblock the blocks like this:
(Clone/Setblock/Execute Commands)

&
%
@
@

@=Player %=Dispencer with enchanted chestplate facing Down &=Redstone Block

Then Remove it using fill and don't let it drop the items.
(Fill/Execute Commands)

his is not a clean solution but I had to do something similar when setting up a red vs blue minigame and I wanted each team to have colored helmets. I cloned a chest at a set location to be above the player, with the dyed helmet in it. Then I broke it with a setblock command with destroy at the end. To adapt it to your case I would clear the chestplate then do the rest. You could also use a dispenser and activate it then remove it. This would put it on his chest slot. (I haven't played Bedrock Edition on a computer just on a Mobile Device and it's been a while so I don't know the exact syntax.)

The syntax would look something like this assuming you tag the killer with /tag @p add Killer

/clear @a[tag=Killer] (Chestplate ID)
/execute @a[tag=Killer] ~~~ clone (x y z of dispencer) (x y z of dispencer) ~~2~ 
/execute @a[tag=Killer] ~~~ setblock ~~3~ redstone_block
/execute @a[tag=Killer] ~~~ fill ~~2~ ~~3~ air

• Sorry my other answer was typed on the spot but this one should work