Hi @markthompson3
Your odata query should look something like this:
<Field> LE <Expression:utcNow()> as illustrated in my screenshot below. I have used Created in my example, at the point of running it will return everything that was created before the current datetime.
Replace the <Field> with the internal name of your field which can be found by going to list settings and then looking at the edit column url. If your field name has spaces in it when its created, you will find your field name will look something like Review_x0020_Date.
LE is the operator, i.e. less than or equal to.
The in single quotes ' ' create an expression with the forumula utcNow(). You'll see this appear in the intellisense, and this will take the exact date time stamp of when the Flow action is executed.

I hope that helps, please shout if there's anything else.