How can I hove the amount of garnishment reduced from my social security

You don't. The court already issued the garnishment order for a certain amount because of a debt you owed.

You would have to convince the people that WON the case.. and got the order to reduce it.. and they have no incentive to do so until the debt is paid off.

Is the garnishment order for a specific dollar figure a week or month ? Or is it a percent?

But agree, if the order does not violate any law, you really don't get it changed.