Losing contacts from android phone happened unexpectedly, so we need to backup them to computer frequently. But as you know, we can't do that directly, we need an android file manager to help. Try Coolmuster Andorid Assistant.
Step 1:Connect Android Phone to pc
The first thing you need to do is to download and install the Android contacts manager on your pc and launch it. The next is connect your Android phone to pc via usb cable. Your device will appear on the screen. The manager would recognise your android device automatically.
Notice: If this is the you connect android phone to the problem on computer, you should enbale USB debugging first, and install a USB driver on your computer, then the app would detect your android phone automatically.
Step 2:Select Contacts and Start Export