Tag line ...
If a pro stepped the mast, there should be a tag line in the conduit to pull a wire through.If there is no tag line and you have another wire (anchor light? VHF cable?) going to the masthead, you can use the other wire to pull a tag line UP through the mast. Attach the tag line to the instrument harness and the harness you removed. Attach a second tag line (to leave inside the mast for next time) and pull both harnesses and the new tag line back down through the mast.Possible problems: The anchor light harness has the connector inside the mast rather than inside the mast. Pulling up on the harness will only unplug the light.

The mast harness is sealed at the mast step with silicone or caulking and you won't be able to move the wires at all.

The mast harness comes out of a stand pipe inside the mast and makes a loop (for water to drip off of) before it goes up the conduit.

If the mast has not been pulled for inspection in the last 5 years, it is time to pull it and inspect all the rigging, tangs, wiring, spreader mounts, etc. You might as well pull it, clean it, look at all the hardware and wiring while it it easy to get to and have no worries until the next 5 year inspection.