Custom Attributes In Login/Register Form Fields

Hi

I’m using Essential Addons’ Login/Register widget to beautify the standard WP effort.
As the widget doesn’t have the ability to force a visitor to use a strong password, I’d like to add a custom attribute to the ‘Password’ field so that when the user hovers over that field, they’ll see a popup message encouraging them to use a complex password.

I’m 99% certain that the message that is set now, ‘Please fill out this field’, is set by WP and not EA.

How could I change the wording for the ‘Password’ field only?
(I’m a beginner, so please bear that in mind!)

TIA