If you're experiencing backlash, or birds nesting, on your spinning reel, there are a few things you can do to fix it. First, take the spool off of the reel and remove any line that's tangled. Next, inspect the spool for any damage or wear. If there are any cracks or damage, replace the spool. Once you've inspected and replaced the spool as necessary, re-assemble the reel and make sure that everything is tightened properly.
If you're still experiencing backlash after following these steps, it's possible that there is something wrong with the drag system on your reel. You can try adjusting the drag, but if that doesn't work, you may need to take it to a professional for further diagnosis and repair.