Started to record over AVI file
When overwriting happens, usually old file is removed. So, new file size is around 0 bytes. Here nothing to rescue.

If you realized your mistake ASAP, in a few seconds, you can press RESET button. You will lost everything unsaved. Perhaps, even file system commit with new data, so old data will be here.

Otherwise, your file lost. You can try to recover file as any other deleted file (possible buy new disk, create sector copy, use any software like R-Studio), but since file here, with new content, this may not help. Try chance in specialized datarecovery company.

Yes, here exists ultimate solution. In theory, you can scan every sector of you hdd for AVI signatures (with AVI it easy possible) and read "RAW" frames from your disk directly. But here two problems:


I don't know good tools for this. I know only one tool, which "in house", written for "in house" usage: http://an-private.narod.ru/video/dvchanger/dvchanger.htm - it dedicated for DV video only. I found some other public available tools like https://www.remosoftware.com/dv-file-recovery, but it not tested by me and I can't suggets it.
Even if you file was in AVI, and you restored frames from your disk, frames may be mixed together due disk fragmentation. So you may get mixed your footages with other files. If you have very costly file, you can try to spend many hours in Premiere to recover it.


Sometimes it's easier to write a program for a specific case and equipment than to use ready-made utilities designed for general purposes. I wrote such a program for a dental camera and successfully restored the video