.flm files do not include the actual audio samples (WAV, MP3) used in the project. If a project uses a custom sample, you must download that sample separately, or the track will show "missing file" errors.
Find the downloaded .flm file (or .zip file if it includes samples) in your Download folder. fl studio mobile flm project files free better download
It won't know which app to use. Instead: you must download that sample separately