There is two (2) different types of agitators used on the Amana washers. I added two images showing the two different types of agitators. If you have the type of agitator as shown in the second image and you are referring to the upper auger portion being loose, there is no fixing it. The upper augur and the lower portion of the agitator is made as one assembly and it would have to be replaced as an assembly.
Now, if you are referring to the agitator being loose where it presses onto the drive bell (key#5) as shown in the first image, the agitator could be split or the drive bell is worn. The agitator is pressed down and over the drive bell. The drive bell is held down to agitate shaft by a bolt and requires a special puller to remove it from the splines of the agitate shaft.
The third image shows the tools needed and instructions.
Resubmit your question with the model number and details for further information if needed.
I recommend calling a service technician to diagnose and repair your washer.