To tighten the brakes on an electric bike, you can follow these steps:

• First, locate the brake lever and follow the cable down to the brake caliper. The brake caliper is the part of the brake system that clamps down on the wheel to slow it down.
• Look for a small adjustment screw on the brake caliper. This screw is usually located on the side of the caliper, near where the cable enters.
• Use a screwdriver to turn the adjustment screw clockwise to tighten the brake. Only turn the screw a little bit at a time, and check the brake after each adjustment.
• If the brake still feels loose after tightening the adjustment screw, you may need to adjust the cable tension. Locate the barrel adjuster on the brake lever, which is usually located near the brake lever where the cable enters.
• Turn the barrel adjuster counterclockwise to tighten the cable. Again, only turn the adjuster a little bit at a time and check the brake after each adjustment.
• Test the brakes by squeezing the brake lever. The brake should engage quickly and firmly, and the brake pads should make good contact with the rim or rotor. If the brake still feels loose, you may need to repeat the adjustment process.
  

It's important to ensure that your electric bike's brakes are functioning correctly before riding, as this can help prevent accidents and ensure your safety while riding. If you're not comfortable performing brake adjustments yourself, it's best to take your bike to a professional bike mechanic for servicing.