Should be in project settings, as I recall it’s called “virtual texture lightmaps” or something. Be aware that SVT has inherent streaming latency that will look like pop-in of the textures as the higher res mips ares streamed in. Unreal’s regular mip streaming is less efficient by being more conservative and so this tends not to be a problem.
This isn’t super noticeable on lightmaps unless you have insufficient padding around your lightmap UV islands.