How to remove the prop

You can get the appropriate pins in the prop not kits sold by minn Kota or thru major retailers.
Trolling Motor Replacement Props Minn Kota Motors
You will find prop nut kits here just follow the link.

remove prop and look !!

Use a gear puller.

Minn kota 74 lbs. prop runs when head turns when rotating motor from centre to right, but stops when you turn motor from centre to left. The light on top stays on.

I have the same trolling motor and the same problem.
It seems the factory grease gets hard inside the motor where the shaft spins and acts like glue. I removed the long screws, carefully pulled the case apart, cleaned out the old grease (which was more like hard plastic) and packed the bearing area with lithium grease. I also lubricated the "O" rings and they were not damaged or brittle so I re-used them and put the unit back together being careful to tighten the screws properly. I have had no problems since. Also be sure to check the connections to the battery, for some reason that motor is very sensitive and wants a really good connection to the battery posts and sometimes all you need to do is re-tighten the connection if the motor does not run at all.
By the way, I contacted Minn Kota regarding the 3Hp and was told "hp" stands for high performance and the motor is not 3 Horsepower.

Fishing string on shaft, runing while out of water(will burn up seals so fast), bent shaft, off balance prop, bad rotor in the electric motor. lots of variables. I bought one that was noisy out of the box, vibrated very bad from the get go

Odds are you have sheared the pin (slides through the prop shaft) holding the prop, or you have damaged the slot on the prop that the pin sits in.

Prop is secured to the shaft with a metal nut, or flat plastic wing nut. Remove the nut to remove the prop. You may have to pry, slightly, the prop from the motor housing. Removed, you will see a whole in the shaft where a pin should be located. If the pin broke, it probably hit the floor when the prop was loosened. If the pin is intact, examine the rear side of the prop and look for damage to the plastic slot where the pin would sit making contact.

If you've snapped the pin, you can make a replacement with a nail using a hacksaw. Replacement pins can also be ordered from Minn Kota. If the back side of the prop is damaged (recess for the pin to sit), the prop is toast. Replacement props are often carried by Walmart, and include a new pin.

If neither part is broken, perhaps the prop was just not seated on the pin correctly allowing the prop to freewheel.

There should be a retainer nut accessible at the rear of the prop (in the center of the prop. Remove this and the prop should slide off.

open up the prop area and look for / remove corrosion