LAX Tower Controller described a Low Altitude event experienced by a aircraft on final for Runway 7R indicating glide slope difficulties; the reporter acknowledging that the ILS configuration was not changed as needed for this late night operation.

Narrative

A B757 received a Low Altitude Alert on approximately 4 mile final Runway 07R. I issued the Low Altitude Alert to the B757 and went over to check the ILS panels. As I was checking the ILS panel; the B757 advised me the glide slope signal was weak; and I noticed that the ILS was set for Runway 25L. I configured the ILS for Runway 07R and advised the B757 that I had reset the ILS. The B757 continued the approach and landed with out incident. During over ocean traffic; I usually leave the ILS for Runway 25L/07R in the west configuration (Runway 25L) since we do not use this runway for arrivals and departures due to overnight noise abatement. I had already completed this portion of the watch check list when the city closed Runway 25R/07L. I must have forgotten to set the ILS for Runway 25L/07R to east configuration (07R) when the City closed Runway 25R/07L. I usually visually check the ILS panels when I provide the relief briefing to the relieving FLM/CIC. While the visually check of the panels is not a requirement; it is a personal preference that I usually perform and did not do this time. Had I stayed with my routine when I was relieved from the GC/CIC position; I would have caught this issue. In the future; I need to stay with my routine.