Much like any other modern compressed archives even 7zip archives can be split to pieces in so called multi-volume archives. When needed, these pieces can be merged back to a single archive using any utility that supports 7zip formats.
Convert Split Multi-volume 7-ZIP compressed file archive (part 1) to 7-ZIP compressed 7z archive.
We have found 3 software records in our database eligible for .7z.001 to .7z file format conversion.
Microsoft Windows software - convert 7z.001 to 7z on Windows
Popular open source file archiver with a high compression ratio
Convert from 7z.001 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 7z.001 to 7z. 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.
Apple macOS / Mac OS X software - convert 7z.001 to 7z on OS X
Mac version of file archiver
Linux/Unix software - convert 7z.001 to 7z on Linux
Command line tool used to create and extract 7zip archives