how to display health bar on hud when picking up item

The easier way would be to control the visibility behaviour of the health bar via blueprints.
Just make sure that in the blueprint where you check the condition ‘health bar can be shown’ you have the HUD with the progress bar in it in a variable, that way you can just get that variable, from there get the health bar (I’m assuming it’s a progress bar), and from there set visibility.
Kinda like this:

137627-health+bar+shown.png