Game-Rip Meshes often come with triangulated geometry.

This is a problem if you want to make modifications to the meshes, since modelling tools work better on quad meshes. It also means that subdivision will not look great.

So can we make a quad mesh from a triangulated one? Yes.
We start with the TrisToQuads Operator. Alt + J

This algorithm will remove edges from the mesh that make up triangles and gives us a quad mesh, wherever that is possible. The trouble with that is that it has no understanding of edge flow and uses an angle threshold to determine in which direction the quads should flow.

This will often lead to what I call "Spin Artifacts", where the edge flow seems to go at a diagonal against the intended flow.

The algorithm will, assuming proper settings, still get the job done 70%. So in general, it still pays off running it and then doing some manual cleanup after.

There are 3 basic tools you will need to get this job done:

Spin Edges: an operator that takes an edge selection and moves the edge connection to the next adjoining vertex, either in clockwise or counter-clockwise direction. Sounds hard to understand? Watch. This is used to redirect polymesh edge flow. It lets us clean up the untriangulation artifacts with ease. While you could map both spin directions to their own keybind, I find it easier to just spam the key. It lowers the required brainpower for the task. The operator is called mesh.edge_rotate. You can also find it in Edit mode: Edge -> Rotate Edge CW / CCW

Delete Edge: what it says on the tin: removes selected edges.

Join: bridges two selected Vertices with an edge. This method, unlike the knife tool, leaves the UVs, Shapekeys and weights intact.

The process is simple and repetitive, but not hard. You look at the desired edge flow on your model and then redirect the edges to follow it. This will involve a lot of spinning, the occasional deleting of an edge at the end of a spin artifact or the reconnecting of a vertex pair with a new edge.

I recommend you use a workspace with a half-and-half split between a 3D View and a UV View Window. The reason for this is that it is much easier to see the edge flow in the flattened state of the UVs. Especially in tight areas like the eyes, fingers, and bodily orifices like eyes and mouth bags.

To make it easier to work in both views, i recommend you add some 3D View Edit Mode keyboard shortcuts to your UV Window. For instance, I have mapped the Rotate Edge CW operator and the Delete Edge Operator to work in UV mode, so I can simply stay on that window and don't have to move the mouse to access these tools in the 3D View Edit Mode.