Check that the needle is not bent and if necessary, replace with a new needle.
Re-thread the machine following the threading instructions in your machine’s instruction manual.
You will also find instructions for your machine online via the Brother solutions centre
Note: We find that Butterfly and Singer Branded needles are often not compatible with Brother sewing machines and may cause issues with your machine not picking up lower thread.
We would recommend using either Organ or Schmetz branded needles.