Following the release of iOS 13.2 last week and the first developer beta of iOS 13.3, Apple has stopped signing iOS 13.1.3. This means there is no way to downgrade your iPhone back to it if you have already updated it to iOS 13.2. The same is also applicable for iPadOS 13.
iOS 13.2 was a relatively major update that introduced a bunch of new features and fixed a lot of bugs as well. It also added Deep Fusion to the iPhone 11 and iPhone 11 Pro that further improves their overall camera quality. However, people who are interested in jailbreaking their iPhone or iPad might have wanted to downgrade their device to iOS 13.1.2 as a jailbreak is usually released for a slightly older release of the OS.
While there is no iOS 13 jailbreak available yet, it is rumored that we could see a checkm8 exploit based jailbreak checkra1n release this week. But since checkm8 is a bootrom exploit, it is possible that it will also work with iOS 13.3. This is something that only time will tell. As of now, if you were looking to downgrade your iPhone or iPad back to iOS 13.1.3 or iPadOS 13.1.3 for any reason whatsoever, you are out of luck.