Mechanics of the Crowding Out Effect

I am calling to the economists out here.

I am studying for the CFA Level I exam and I am reading this sentence:

"Increased government borrowing will tend to increase interest rates, and firms may reduce their borrowing and investment spending as a result...This is referred to as the crowding-out effect"

I obviously understand firms reducing borrowing and investment because of higher cost of debt. However, I don't understand how increased government borrowing will increase interest rates.

What are the mechanics that cause interest rates to increase because increased government borrowing?