I confirmed that "F2 z 00" sets the playback position e.g. when sending it to Renoise (in this case, the Zxx parameter specifies the offset in the song in 16th notes). However, the MIDI implementation chart of the Volca Sample suggests that it cannot actually receive Song Position commands.
Maybe it supports MMC commands instead? Try sending this macro: F07F7F064406010000z0000F7 (Zxx parameter = song position in seconds)
Edit: I've attached a module that sets up the MMC command for you already. It will set the song position to 0 seconds, 1 second, 2 seconds... as you can see in the pattern. Be sure to select the correct MIDI device in the MIDI I/O plugin!