Idk how the command works so could you re-message me the command and use the username N3o_V2 and 2 hearts?

By default the alias is lifesteal so that's what I will use

I am going to assume that the player isn't online so I have used NameMC to grab the users UUID (b64b6ee631f74436a48c99c724adad92)

Also I am unsure if you want to loose, gain or set the user to only have 2 hearts so I will give you the commands for all of them

To take two hearts you can preform:
/lifesteal set b64b6ee631f74436a48c99c724adad92 4

To give two hearts you can preform:
/lifesteal set b64b6ee631f74436a48c99c724adad92 -4

To set the players health to 2 hearts you can preform:
/lifesteal set b64b6ee631f74436a48c99c724adad92 16

Hope that helps <3