Last month, as you may know, I was a volunteer on the occasion of my favorite band's concert in Katowice.
#Last month, as you may know, I was a volunteer at a concert occasion of my favorite band's concert in Katowice.
The last month, as you may know, I was a volunteer on occasion of my favorite band's concert in Katowice.
#Last month, as you may know, I was a volunteer on occasion of my favorite band's concert in Katowice.