How to extract .backup files created by android stock recovery?

I'm using Coolpad note 3 lite, running Android 5.1. I created internal memory backup using stock recovery. Files were created in this format:

1. userdata_yyyymmdd_HHMMSS.backup = 2GB


2. userdata_yyyymmdd_HHMMSS.backup1 = 2GB n. ...


3. userdata_yyyymmdd_HHMMSS.backup5 = 1.53GB

Is there any way to extract the files to PC? I couldn't see file header mentioned here. Another user referred a method, which I couldn't understand.

• Android 5.1


• TWRP installed


• Rooted


• FAT32 internal & SD card.


• Tried Titanium backup and it don't recognize the format.

Edit:

1. Tried to do a stock recovery backup and replace the files. While trying to restore stock recovery not showing SD card, although it takes backup in SD card during backup in same session.


2. 7Zip Windows opened the merged .backup file. It shows "2.ext".



3. Mounting 2.ext in Ubuntu shows nothing even though file space is occupied.


4. When trying to open 2.ext using 7zip, I see lot of files in similar name and opening them in 7zip again shows again same file names....

Now how do I recovery files from this 2.ext?