Customise Email Content

I’ve customised the email subject line and I’d like to customise the content too but not sure how to tap into the loops. Ideally, if an update is available, I’d just like the email to say:-

Wordpress needs updating to Version ABC

Updates are available for these plugins:-
Plugin Name (new version x.y.z)

Updates are available for these themes:-
Theme Name (new version x.y.z)

What needs to go into the filter to achieve this please? Thank you!