If you need to produce subtitle in Cavena format (.890) from SubRip subtitle sources (.srt), you will need to use some of the dedicated subtitle editors like Subtitle Workshop, WinCAPS or similar. But overall, Cavena subtitles are not that well supported so your options are limited.
Convert SubRip video subtitle format to Cavena subtitles file.
We have found 2 software records in our database eligible for .srt to .890 file format conversion.
Microsoft Windows software - convert srt to 890 on Windows
A free subtitle editor
Convert from srt file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned srt to 890. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A subtitle editor