Cloud backup is recommended. If unavoidable, please back up as follows:
1) Install "ES File Explorer" on Google Play Market and run.
2) Go into Settings -> Display settings then check "Show hidden files" options.
3) For Samsung mobiles, move to path "/storage/emulated/0/.cleancall2/.records/" 
- For each device, path except "/.cleancall2/.records" can vary.
4) Select all files, push "more" button then select "Compress".
5) Select the compressed file, and then click "more" button then select "Move".
6) Move compressed file to path "/storage/emulated/0" (The path stands for the path of the main terminal, it may vary from devices)
7) Connect PC and mobile with USB. (You may need USB driver software on each devices. Please contact the manufacturer.)
8) Check the compressed file in the default path of the connected cell-phone memory.
9) Copy compressed file to PC.

※ To move the backup file back to the device after phone initialization, you can proceed in the reverse order of how to back up the recorded file.