Open the Files app
Tap Browse
Tap On My iPhone or iCloud Drive
Tap Downloads
Open the file you want
Open Safari
Tap the downloads icon in the top right or next to the address bar
View recent downloads
Open the app you used to download the file
Check its download or library section
Open the Photos app for downloaded images or videos
Open the Music app for downloaded audio
Open the Books app for downloaded PDFs or ebooks
Use Spotlight Search and type the file name if you cannot find it