Claw. Bucket. Reinforced net. Submersible ROV. Trained sea life. Anything that's not a magnet.

Supposedly it's in pieces from the impact. Small samples would be fine to locate and collect via ROV with a metal detector on it to check below the silt.

If they want mass extraction after that, then potentially a form a dredging could be used (vacuum and filter could work to leave the sand and silt on the bottom).

Core sample via remote controlled submarine. Magnets sounds goofy. I suspect he knows something we don't.

Arcade claw, with coin slot and all.

Too bad they scrapped the submarine lifting grapple equipped Glomar Explorer

https://en.wikipedia.org/wiki/Glomar_Explorer

Inflatable ballasts

Tractor beam.