Update new version
How can I download a previous version of iOS software?
iPhone 7 Plus, iOS 13
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Top-ranking reply
More information would likely help you get a better response..
You say 'could not install it', why couldn't you install it? What happens when you try?
Here is a user tip that may help with updating issues
Updating iOS: common issues and solutions - Apple Community
If your details are correct and you are running iOS 13, then you are at least 2 years behind with your updates. You may need to update using a computer.