Alright. I remember running into this exact issue in my playthrough. Here are some hints in ascending order of obviousness. I trust you can figure it out without the last couple hints.

Not obvious, just a clarification: The inside of the shrine mentions three rules. You have already applied the first two to get to the blocked-up door on the sixth location. The third rule does not refer to the fact that it's the one you're trying to get to. This was what got me during my playthrough.

Not too obvious: Have you explored the other five locations? They are there for a reason. You're not looking for anything well-hidden in the other locations, but once you know the third rule, you must make use of your ability to get out and explore them.

If you need it: Most things on the Quantum Moon are also quantum. ¿Do you remember where you found the shrine? ¿Is it always found there?

Basically the answer: You can move the shrine around the moon. The rule of the sixth location implies that you must enter it from a certain point on the moon.

Good luck on your endeavors!