Many MT6739 phones use a Dead Boot Repair trick:
Guide to Flashing Firmware on MediaTek MT6739 Devices The is a popular entry-level 4G chipset found in many budget Android smartphones. To update firmware, fix bootloops, or unbrick these devices, you need the SP Flash Tool (Smartphone Flash Tool), a free utility specifically designed for MediaTek (MTK) chipsets. Essential Requirements mt6739 flash tool