The E-F1 error on a Brother embroidery machine indicates a problem with the upper thread sensor. Here are some steps you can take to fix the issue:

1. Turn off the machine and unplug it from the power source. Wait for a few minutes before plugging it back in and turning it on again. This can reset the machine and clear any temporary glitches.
2. Check the upper thread. Make sure the thread is properly threaded through the machine and there are no obstructions or tangles in the thread path.
3. Check the needle. Make sure the needle is properly inserted and not bent or damaged.
4. Check the thread tension. Make sure the thread tension is set correctly for the type of fabric and thread you are using.
5. Check the upper thread sensor. Make sure the sensor is clean and free from any debris or dust. If it appears to be damaged, it may need to be replaced.
6. Check the machine for any signs of damage or wear. If any parts appear to be damaged or worn, they may need to be replaced.

If these steps do not solve the E-F1 error, it may indicate a more serious problem with the upper thread sensor or the machine’s internal components. In this case, it is best to contact a qualified technician or the manufacturer for assistance.