I have been here... I was her?? Did you mean I was here? If so, then there is no difference in either sentence. You can use either one as long as you are talking about a place that you have been to before and are now back at again.

' I was here' you talking about past .while ' I have been here ' you talked about bresent perfect

It's a very simple difference: use "I was here" and add the time in the past. You are talking about the past. If you don't include the time, use "I have been here". We use present perfect to talk about the present, and that includes your experience from the past to now.