How can I make my white LED strip light warmer?
The cheapest, laziest way (that would actually work) is to obtain some cinematic gels (they are sheets), such as those made by Rosco.   Cut them into strips or squares, affix any way practical.

The better, long term approach is to spec better LED strips.  LED strips come in a huge range of product qualities.  By and large, consumers either pay waaaaay too much for mediocre quality strips (I've seen companies charge $90/metre with a straight face), or very low prices ($7 per 5 metre roll) for "fell off a truck in Shenzhen China" quality strips.  Either one may have poor accounting for CRI, overall brightness, etc.  

Aside from color temperature, there is also CRI (Color Rendering Index), a percentage scale of how close to natural or tungsten light it is.  CRI is compensated for what human eyes see, so a light can be quite uneven on a spectrum analyzer and still have a very high CRI.  Machine eyes don't see light the way human eyes do, which may be a problem if machine eyes are involved.