Distortion on DAE to obj High poly clothes conversion issues

Hi. I think you are misunderstanding the terms you are using and, as a result, googling for the wrong things. What you need is a tutorial about adapting cc for ts4, so search for things like "covert to the sims 4", "from other games", "from the sims 2* to the sims 4"
* in ts2 the default pose differs from that of ts4, so they should show you how to change that pose.

When you save something in a 3d modeling software, it is saved in a file format that is native to this software. For blender, it is .blend, for Maya, it is .mb, etc.
However, to use your creation in different software, you need to export it in the file format that the other software recognizes.
There are a few cross-platform file formats that all 3d modelling software recognize: .obj, .dae, .fbx. The difference between them is in how much information they store.

Once you import the .dae file in the scene, it's no longer a ".dae file". It is a 3d model in the .blend file. And it is a .blend file that s4s needs you to import in it because .obj, .dae, and .fbx, do not store all the information needed for the item to function properly in the game.

Anyway, the reason proportion editing is not working for you is because it is disabled. The icon needs to be blue.

You also should dramatically decimate the item first because s4s will not import something that has 20 times more polygons than any maxis item. And before that, you'd need to remove all inner geometry, which would reduce the polycount by half.

I recommend you to just not do this, seriously. The mesh is too high poly for you to remove the inner geometry in one click with Remove doubles. The Decimate will ruin the mesh completely before you'll get to the acceptable polycount. Changing the rest pose of the garment is difficult and requires you to already know the basics. This is like setting yourself for failure from the start.
If you want to have a similar item in your game, consider learning how to frarnkenmesh instead. Not only is this easier, but you'll also learn the basics with no obstacles.