How to write regex find square brackets?

I have a piece of text and need to find lines that look like this:

[DAY] Today 20/08/2020
[DAY] Today 26/09/2020
[DAY] Today 26/09/2020
[DAY] Today 26/09/2020
[DAY] Today 26/09/2020

In the second half I could use "Today. *" but I don't know how to find the string in square brackets [DAY], please help me.