I have created the process for changing the cloth to make it easy and simple.
The step includes
- setting the Rig
- accessing the rig in code
- changing the cloth by pressing E

The first and important step will be setting up the rig. To set up the rig we have to click on the AVATAR window > Rig Builder > Block Avatar

Cool, now you can see the dummy character in your game.

Now select the rig in the Explorer window and add the pant and shirt objects into it. After doing that, you need to select good cloth for your character. Go to the Roblox marketplace and find good clothes for your character. click here

Copy the link and select the cloth object in your game. In its property panel, you can find ShirtTemplate and add a link into that.