NASA decided rather late to take a flag to the Moon on the Apollo 11 mission. In fact, they were so late that the package containing the flag was only attached to the leg of the LM on July 9th, two days before launch:
Because the final decision to fly the flag and attach the plaque was made so close to the launch date, a Lear jet was chartered to fly Kinzler, George Low (Manager of the Apollo Spacecraft Program), Low's secretary, the flag assembly, and the commemorative plaque to KSC before the launch. The flag and plaque were installed on the LM of Apollo 11 at 4:00 in the morning as the spacecraft sat atop its Saturn V rocket ready for launch. Kinzler had written an 11-step procedure for mounting the assembly on the ladder and personally supervised the installation.
The Apollo stack had left the Vehicle Assembly Building already in on May 20, and the launch tower does not seem to provide access to the LM: at the level of the fairings covering the LM there seems to be only some umbilicals connected to the stack; I cannot see a bridge that allows people to access (although the scale can be deceiving).
How did they get to the LM to mount the flag package and plaque?
I assume that there were numerous access points to the stack, since between May 20 and July 16 they were doing numerous tests and they'd need access to various parts of the stack to fix issues if needed. Perhaps the photo below is not showing those access points.
I'm looking for photo's and or diagrams that show how they could access the LM under the fairings while the Apollo stack was on the pad. Better even photo's showing the flag and/or plaque being mounted.
Apollo 11 rollout; no obvious way to access the LM from the launch tower (source: NASA)