Both the ASS (Advanced SubStation Alpha) and SRT (SubRip) formats are pretty common video subtitle file formats and ass to srt conversion can be easily achieved with any of the subtitle converters or editors.
Open ASS file Open SRT fileA subtitle editor for OS X (macOS)
A subtitle editor for GNOME
A program for editing of text subtitles for videos
Small tool for macOS, which allows users to convert ass, ssa, s2k, smi, sub files to SRT format
A software for subtitle editing and preparation
An online converter for subtitles