If you're looking to shrink your leather, there are a few methods you can try. Perhaps the most common is to simply soak the leather in water, then dry it off quickly with a towel. This will cause the leather to contract and become smaller. Another method is to heat up the leather - either with a hair dryer or by placing it in direct sunlight - which will also make it shrink slightly.
Of course, these methods are only temporary - if you want to permanently shrink your leather, you'll need to take more drastic measures. One option is to repeatedly soak and dry the leather until it reaches the desired size; another is to use special chemicals that will break down the fibers and allow you to reshape them as you please. However, both of these methods require quite a bit of time and effort, so be prepared for some trial and error before you achieve the perfect fit.