how can i get xcode on my high sierra 10.13.6
First, find the appropriate version from Xcode wiki.
Seems the latest version of Xcode which runs on High Sierra 10.13.6 is 10.1.
You can download old Xcodes from More Downloads page.
But please remember, you need Xcode 11 or later to build an iOS app for App Store,
meaning you need to upgrade your macOS (or Mac) to 10.14.4 or later to build App Store apps.
Seems the latest version of Xcode which runs on High Sierra 10.13.6 is 10.1.
You can download old Xcodes from More Downloads page.
But please remember, you need Xcode 11 or later to build an iOS app for App Store,
meaning you need to upgrade your macOS (or Mac) to 10.14.4 or later to build App Store apps.