Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 3358 (unattended-upgr)

The error message you encountered indicates that the package management system (`dpkg`) is currently being used by another process, specifically the `unattended-upgr` process with the process ID 3358. This usually occurs when an automated upgrade process is running in the background.

To resolve this issue, you can try the following steps:

1. Wait for the current process to finish: The lock is in place to prevent multiple processes from interfering with each other. Give it some time, and the lock should be released once the previous operation is completed.

2. Kill the conflicting process: If waiting doesn't resolve the problem, you can terminate the conflicting process manually. To do this, open a terminal and run the following command:

   sudo kill 3358

3. Remove the lock files: If killing the process doesn't work or if it's not a critical process, you can remove the lock files directly. Use the following commands to remove any existing lock files:

   sudo rm /var/lib/dpkg/lock-frontend
   sudo rm /var/lib/dpkg/lock

After performing these steps, you should be able to use `dpkg` or related package management commands without encountering the lock error.