If it’s a Poser format file (CR2,PP2,HR2,PZ2 etc) then I open it in a text editor (they are plain ascii) and change the pathway’s to point to the file, that way I can check the formatting is correct as that can cause DS to throw a “missing file” warning too, the pathway should look similar to this -
":Runtime:Textures:Vendor:Product:Texture.ext"
DS native formats (DS,DSA,DSB) I use the Script IDE plugin, it used to come in the Script Dev kit but it’s now built into DS4, and edit the pathways in it, they should look similar to what you see in a Poser file, but with an / instead of an :
DUF & DSF files are ascii so they can be edited in a text editor, they may be compressed so you might have to unpack them first, use the batch converter plugin in DS4, the pathways in these are the same as the other DS files.
.DAZ scene files you can’t edit, so either do as Marieah, or locate the textures in DS and then resave the .DAZ scene file.