You can flash this device using testpoint methode.
Newest oppo mediatek implement ARB, so make sure your firmware version is same or highest than firmware already flash in device. Secure boot its limited user for writing certain area, like bootloader and security partitions, exept boot, recovery, system, cache, and userdata. You can write unique partitions in above via Isp methode.
For imei, you can try repair in AT-mode, you can search this forum how to do that.