How to apply style to same words using find and replace

I have a document I need to format.

Let’s say I want to put Day 1, Day 2 etc as Heading 1. Since I have 100 of them, is there an easy way to apply a style to all paragraph with the word starting Day? I know you can use the alternative find and replace extension but it seems you can only replace one style with another style, not to apply a style to particular word/paragraph.

I can do this in microsoft word easily but not sure if there is such a function in libreoffice.

To search for complete paragraphs starting with the word “Day”:
Open the F&R dialog.
Enable RegularExpression.
Enter ^Day.*$ (case insensitive) or (?-i)^Day.*$ (case sensitive) behind Find:.
To change formats and/or styles:
Leave the multiselection you get untouched and make the style assignments you want.

If you left the F&R window open, and want to set an attribute by pressing keys on the keyboard, you need to first click outside of the text on the Writer window (TitleBar e.g.) to move the focus to the ComponentWindow.