if you don’t know where to start, start by learning about SLAM (simultaneous localization and mapping).
that usually has a much richer “needle” to find (in the haystack), and it has a previous pose to refine continuously, so it usually doesn’t have to find its own location from scratch.
however, in that area of research, there might be approaches for locating/pose-estimating a subset of a point cloud in the larger point cloud.