cub cadet model 1525 hydrostatic lawn tractor with 15 hp kawasaki engine that is seized. How can it be fixed?

Depending on how long it has been seized, it might be kinda easy, or a huge job. Start by removing the spark plug and spraying a large quantity of penetrating oil directly into the cylinder. Let it sit for a day and then try turning the crankshaft with a wrench. Don't try using the starter until you can turn it easily by hand. After you get it turning you can pour in a little motor oil and turn it some more. When it is easy to turn, let the starter spin it for a while. Put the spark plug back in and see if it will start. The biggest potential problem is that the rings might be "set" and it won't have good compression, and it might also burn oil. If that is the case, an engine rebuild will be in order.

take out the spark plug and add a couple tablespoons of transmission fluid into the engine. You can also add some through the carb. Let it sit a while, and then try turning the shaft with a pipe wrench. May be a lot more wrong also. I am going through the same thing right now.