How do you reverse the direction of a text preset ?

As Steve already mentioned "Stretch and Slide" is not a text animation presets. There is no existing text animation preset that matches the look of this Transition and Movement preset. After reading this post you should be able to create your own text animation preset the does the very same thing by applying the same math and logic to the available text properties under the Animate menu at the top of a Text layer.

When you are trying to figure out exactly what is going on in a layer just select the layer and press the U key twice. I could see all of the expressions and the complete layout very quickly. I started at the bottom and disabled the expressions then I started with just the Anchor Point expression. It only took one scrub through the timeline to see what was happening by just looking at the value. A quick glance at the expression revealed the source of the movement. That is all that it took. 

A simple linear interpolation method was used to convert the Stretch Master Control slider to values that would move the Transition>Anchor Point from comp width to comp center. The linear method is written like this:

linear(t, tMin, tMax, value1, value2)

"t" is the value of the property you are reading. In this project that is the Stretch Master Control Slider that is added to the layer as the first effect. "tMin" and "tMax" are the minimum and maximum values you expect from t. "value1" and "value2" are the new values you want to deliver to the property. This is the original Transform>Anchor Point expression:

transComplete = effect("Stretch Master Control")("Transition Completion");
linear(transComplete, 0, 100, [thisLayer.width, thisLayer.height/2], [thisLayer.width/2, thisLayer.height/2])

If you check the value for the anchor point you'll see that the X value, the first part of the array, places the anchor point at the right edge of the comp and moves it to the center. That makes sense when you check the Anchor Point values. This expression also locks the Y position to the center of the layer. 

To change the movement from right to left to left to right you need to start with the "value1" set to zero. That is all there is to it. This is the modified expression.

transComplete = effect("Stretch Master Control")("Transition Completion");
linear(transComplete, 0, 100, [0, thisLayer.height/2], [thisLayer.width/2, thisLayer.height/2])

 The layer now comes in from the Right instead of the left. All that is left to do is enable the other expressions. I hope this helps you figure out how to analyze what is going on with a layer and then change the properties you need to so that you get the results you want.

A couple of things to note:

The preset you're looking at is not a dedicated text preset - it's a general effects preset. Yes - it will work with any layer, including text, but it's not really designed for text. I've had a quick look at it, with a view to your request to change direction. Frankly it would be much easier for you if you just keyframed it directly. All that's basically happening is ax X scale change and an X position change. 4 keyframes in total. See if you can create it yourself.

If you want to explore dedicated text presets, look under: Animation presets > Text >...  there's a load of them.