It seems the only way to convert .prv files to .pvs files would be to use standard working procedure in SoftMaker Presentations and use the template (.prv) to make a presentation document (.prs). Likely, this can only be done in the default program and in no other 3rd party software.
Convert SoftMaker Presentations presentation template file to SoftMaker Presentations document file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert prv to prs on Windows
A innovative presentation program from Softmaker Office suite
Convert from prv file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.