Hello @venkadeshcivil,
If you have made changes to the main theme files, the customization will be lost upon the theme update.
However, no settings / theme options and setup will be lost unless the theme files has been modified.
If you have made changes to the theme files itself, you will need to add ALL the customizations / changes in the parent theme to your child theme and only after that update the parent theme accordingly.
If you have any queries further, please feel free to post them here.
Best Regards !!