Unpack Mini ADB & Fastboot with Drivers file and install both.
Unpack Oppo Qualcomm Drivers.
Unpack OPPO A37 firmware with flasher that you downloaded before.
Changing firmware in the phone will erase all of your data.
All described operations you are doing at your own risk.
If want saves your data do a backup before start.
Firmware Update / Change / Repair in OPPO A37
Turn off phone by the Power button.
Hold Volume up and Volume Down buttons in OPPO A37 phone and connect USB cable from computer to phone.
Wait few seconds and realise Volume buttons.
Open device manager and check if drivers are installed correctly. If not tap on unknown device and press right mouse button and select install drivers manually and then select directory where you unpacked Oppo Qualcomm Drivers downloaded before.
If all is installed correctly like on the picture can go to the next step.
On computer go to the directory that you unpacked OPPO A37 firmware and start "Msm8x39DownloadTool.exe" file.
In application select checkbox "Reset when download" option.
That everything you are ready to change firmware in your OPPO A37 phone.
Press the Start button to start firmware change, update, repair process.
Firmware change operation started, wait until you see green text in the application and phone reboot to normal mode.
After you see USB download complete in the application you should tap Exit button and disconnect USB cable. Just wait until phone turns on to welcome screen.
This can take about 10-15 minutes.
Congratulations, all goes well and without any problem. Perfect job.