Modding:Fixing UV errors

This tutorial is from a post shared by tyvianpear in the DbtR Discord server.

Steps

Open two instances of Blender; 2.79b and 3.X (latest)
Install LaughingLeaders' Blender Helpers for 2.79b into 2.79b
Open your model in 3.X first
Copy and paste the entire model and all its meshes into 2.79b
Minimize (or close) 3.X, we won't need it again until the end
Open up another window next to the Properties Tab by pulling on one of the stripped triangles in the top corner
In the new window, click on the Properties button under the Project Outline, choose UV/Image Editor

Click on the mesh you want to check first (to be on the safe side go through each mesh one by one)
Hit TAB to go into Edit mode
Click on the vertical Helpers tab and make sure that the Select All Problems box is checked
Click on Check UV Triangles

At the very top of Blender, you'll see a notification telling you how many UV problems were found. They will also highlight them in orange on your mesh and in the graph on the right

To the left of your model, you'll see Remove Doubles in the Tools tab
Click on it and you'll see a message at the top, Removed 0 vertices because the merge distance is too short to combine any of the overlapping vertices
Try changing the merge distance incrementally as small as possible. Somewhere around 0.0004 you'll see Removed X vertices at the top
Keep an eye on your mesh and make sure it's not getting too distorted
After each vertex removal/merge, select and deselect (CTRL-A in edit mode) the mesh and repeat the earlier steps of Check UV Triangles and Remove Doubles of vertices

Not all UV errors will show up on the graph, so keep an eye on the notification at the top that tells you how many UV errors you have
When you've merged all the vertices causing problems, you'll see No UV problems found at the top

After you have done this for each mesh in your model, copy and paste the entire thing back into 3.X
Export as .DAE