WARNING: this won't wipe your personal data, but it does appear to clear WiFi passwords. If you haven't already, enable Developer Options and USB Debugging. Next, download the Oppo_Free_Unlock_v1.0.zip file from the attachments and extract it somewhere. Before you run anything, though, there's a little preparation that needs to be done. Open Device Manager and expand the Network Adapters category. Find your Ethernet adapter and double click it to open its properties. Go to the Advanced tab and find the Network Address option in the Property pane. Under the Value pane, select the radio button next to the text box and paste in the following: 704D7B61ABCD. If you don't have an Ethernet adapter, try to find another network adapter here that has the Network Address property. It may help to install VirtualBox, since it will add fake Ethernet adapters. Close the properties window and close Device Manager. Go to where you extracted the unlock tools. Open Sec5.exe. Make sure your device is in MTP mode, and then press the Unlock button. After about a second, a string of numbers and letters should show up in the left pane. A few seconds later, "OK" should start flashing in the right pane. Press "Stop unlocking" and close the window. Open the phone app on your device and dial *#3954391#. Then dial *#391#. A screen should come up with a whole bunch of regions listed. Choose the first one: "Multilingual Version Ex". Your phone should now reboot. Once it's rebooted, your region will have changed and you should be able to use the In-Depth Test app to unlock your bootloader.
In theory, changing your region like this should work on any OPPO/Realme device running at least Android Pie (9). It may even work on earlier versions. NOTE: This will not work for Chinese variants. These codes are filtered and will only work for international variants. However, the Chinese variants should be immediately unlockable.