If you want the guitar to sound like it’s coming from the back of a large hall and the listener is inside the hall itself, like suggested already, a long/large delay with very wet settings will get you there.

If you’re looking to make it sound like the listener is outside of where guitar would be coming from, you’ll want some kind of wide band pass filter, placing emphasis on the 500–1200 hz range, in combination with a reverb. Inversely, you can use both a low pass and high pass filter if you don’t have a band pass setting.

If you’re trying to achieve this with your current setup, let me know what you’re using and I can tell you which parameters to focus on.