Assuming you are referring to a quick connect fuel line connector, there are a few ways to fix a fuel line connector.
If the connector is leaking, the first thing you will want to do is check the O-ring. The O-ring is located on the male end of the connector and is responsible for sealing the connection. If the O-ring is damaged, it will need to be replaced.
If the O-ring is not the problem, or if the connector is not sealing properly, you may need to replace the entire connector. Quick connect fuel line connectors are available at most auto parts stores.
To replace the connector, first disconnect the fuel line from the connector. Then, remove the old connector by pushing on the release tab and pulling the connector apart. To install the new connector, simply push it onto the fuel line until it clicks into place.