Are you talking about something like this:

Node(
        package='rosbag2',
        node_executable=' ',
        node_name='rosbag2_node ',
        arguments=[' ', ' '],
        parameters=[{ ' ': }],
        output='screen'),

If you know how to start a node from terminal then you can also launch it in a launchfile. You can simply add the Node(), to the other launch_descriptions inside:

return LaunchDescription([
...
])

You will just have to import

from launch_ros.actions import Node

I left the fields blank, because I haven't used rosbag2 and don't know the name of the executables or parameters etc., but hopefully this helps. If I misunderstood your question please let me know.