These symbols are downloaded automatically by XCode every time you connect your device to your Mac via USB, while the XCode Application is open.
To download symbols for your device, please follow these steps:
1- Connect your device to your Mac.
2- Open the XCode Application.
3- Open Devices & Simulators (Window → Devices & Simulators | ⇧⌘2.)
4- Check that your device is recognized as connected:
Note: if you see the message "Development cannot be enabled while your device is locked", your Mac is not a "Trusted" computer. Please follow these steps to fix it.
5- Wait until XCode debugger support process finishes. This may take up to several minutes.