Apple has stopped signing iOS 7 almost a decade ago. This means a "standard" restore via iTunes or Finder is impossible. You generally have two scenarios:
This guide is for educational purposes only. Downgrading an iPhone 5s to iOS 7 carries significant risks, including rendering the device unusable (bricking), security vulnerabilities, and loss of data. Proceed at your own risk. I am not responsible for any damage to your device. how to downgrade iphone 5s to ios 7
This is the most dangerous step.
You'll need to have SHSH blobs saved for iOS 7 for your device. These blobs are crucial for the downgrade process. Tools like TSSSaver (by tsschecker) can help you save or fetch these. Apple has stopped signing iOS 7 almost a decade ago
If you are determined to try and believe you have the necessary "blobs" or a compatible jailbroken state, the general (highly technical) outline is below. Downgrading an iPhone 5s to iOS 7 carries