What phrase can be used to accept an unneeded apology?

I need a word to say to the person that apologizes for something that they didn't do but feel responsible for. The word word mean: "I accept your apology, but it is not needed. (you, are entirely fine!)"

You might say "Not at all!" in this situation: you're strenuously denying that there is any apology needed, which isn't actually obvious from the usage (which on the face of it looks like a non sequitur).

You could also say "No apology necessary!". It can be tricky to pull this off, as it actually focusses attention on something that might actually just be almost a form of reflexive politeness rather than an actual apology. As implied by my comment above this is very common in the UK, where people will apologise as a way of communicating all sorts of things, from "I'm genuinely sorry for what just happened" to "Get the f*ck out of my way" (the latter obviously being an example of passive-aggressive behaviour).

Possibly more "safe" is a simple "No worries" or "no problem", which just moves everyone past the awkward apologising situation as quickly as possible.

All options are best done with a smile, if you can make it look sincere.

EDIT: if you are visiting the UK, you might want to research "British Politeness" some more, as it's a complicated subject, where not all is as it seems, although it's still easier than "Japanese Politeness" I think.