Method #1 (FlashTool):
  1. Run SP Flash Tool
  2. Go to Format tab
  3. Select Manual Format Flash
  4. Now enter this values
    • Begin Address[HEX]: 0x6a00000
    • Length[HEX]: 0x100000
  5. Click on Start
  6. Plug-in powered off phone to PC
  7. Wait for the operation to complete

Method #2 (TWRP):

  1. Flash TWRP using SPFT
  2. Copy FRP Script zip to SD Card
  3. Flash it using the TWRP

Now phone won't ask you about the google account anymore.