To install or reinstall the operating system (OS) on your MacBook Pro M1 (13-inch) 2020 model, you can follow these steps:

1. **Backup Your Data**: Before proceeding with the OS installation, it’s crucial to back up any important data on your MacBook Pro. You can use Time Machine or any other backup method of your choice to create a backup of your files.

2. **Download macOS Installer**: Ensure that you have access to a stable internet connection. You can download the macOS installer from the Mac App Store. Open the App Store, search for “macOS,” and download the installer for the version of macOS you want to install.

3. **Create a Bootable Installer**: Once the macOS installer is downloaded, you can create a bootable installer using a USB flash drive. Follow Apple’s official guide or use third-party software like DiskMaker X to create the bootable installer.

4. **Connect the Bootable Installer**: Insert the USB flash drive containing the bootable installer into a USB port on your MacBook Pro.

5. **Restart Your MacBook Pro**: Restart your MacBook Pro and hold down the Option key immediately after hearing the startup chime. This will boot your MacBook Pro into the Startup Manager.

6. **Select the Bootable Installer**: In the Startup Manager, you should see the bootable installer listed as an option. Use the arrow keys to select it and press Enter to boot from the installer.

7. **Install macOS**: Once the macOS installer loads, follow the on-screen instructions to proceed with the installation. You’ll need to select the destination disk where you want to install macOS. Choose your MacBook Pro’s internal SSD and proceed with the installation.

8. **Complete the Setup**: After the installation process is complete, your MacBook Pro will restart. Follow the on-screen instructions to set up macOS, including selecting your language, setting up your Wi-Fi network, and signing in with your Apple ID.

9. **Restore Data**: If you backed up your data using Time Machine, you can use the Migration Assistant during the macOS setup process to transfer your files and settings from the backup to your MacBook Pro.

10. **Update macOS**: After completing the setup, it’s recommended to check for and install any available macOS updates to ensure that your MacBook Pro is running the latest version of the operating system.

By following these steps, you can install or reinstall macOS on your MacBook Pro M1 (13-inch) 2020 model. If you encounter any issues during the installation process, refer to Apple’s support documentation or contact Apple Support for assistance.