How can I update my app to make it compatible with older ios versions?

Set the deployment target for the app's target to the earliest iOS version you want to support. Select the project file from the project navigator on the left side of the project window to access the deployment target. If you need more detailed instructions on setting the deployment target, read the following article:

https://www.swiftdevjournal.com/supporting-older-versions-of-ios-and-macos/