There is no native way to un-precompose. This script is essential.
The plugin was created to simplify the process of un-precomposing layers, saving users time and frustration. With Un Precompose, users can quickly and easily break down precomposed layers into their individual components, making it an essential tool for any After Effects user.
Whether you download the free legacy version or purchase the latest release, installation is identical:
Un-PreCompose plugin for After Effects is a widely used, pay-what-you-want
If you cannot find a working free download, consider these alternatives: