Hi,
How do I fix this texture stretching? Thanks in advance.
Looks like your mapping is messed up somehow. It might be your UVs or your texture coordinates.
What do you know about UVs ? These look like faces which haven’t been unwrapped properly. You don’t have to use UVs, you can also set your image texture node mapping mode from “flat” to “box”, but this comes at the cost of less control.
It looks like you have extruded areas after uv unwrapping, that’s why the new faces act like their uvs are infinitely thin. If you are using a PBR texture that is tiled seamless, just mark seams correctly if not already done it, and uv unwrap it again. You can also use smart uv project if you don’t like marking seams, but it will cause visible seams in the texture at edge areas. BUT if you are using a projected image texture that is not meant to be tiled, you must go to edit mode, set the selection method to faces, then select all the faces in the problem areas, unwrap only those faces, then in the uv editor move, rotate and scale them into an area that has the most suitable texture on it in the image. 
Except for the wrong UV in the UV, I think you just need to set the wrong UV again after fixing it with Pin.
However, the UV does not look complex or important.
I think it would be easier to reset UV for the whole thing.
Thanks, Janne. I will try marking seams and report back.
Hi Janne,
After marking seams on the object, I was able to properly texture it. Thanks for your help. I will definitely use Mark Seams more going forward.