Undo the big brass nut on the end of the steering cable/through tube. Disconnect the drag link from the steering arm. Use a hammer and soft drift/copper mallet to tap the shaft out of the tube. If it's very tight but you can get it to move, lubricate the part you've managed to expose and then tap it back in. Continue working it until the shaft is free.
Clean it all up, if it is still usable, and grease it with water resistant grease. Replace the seal at the output end before refitting the cable shaft.
If it looks in poor condition generally, replace it.
Service it properly in the future bozo.