iCloud backup

so basically I got the iOS 14 beta and I wanted to get the iOS 13 back because it made my phone lag too much and it caused I to be very slow. So I found out how to do it and I backed up my phone so I can get everything back and that backup didn't show up when I was setting up my phone . it showed me a backup from august of last year so now I don't have anything from the last year even though I backed it up. can you please tell me how to fix this.