Hello my name is Mike and thanks for using Just Answer. You first need to shut off the water to the faucet by turning the valves under the sink fully clockwise. Do this while the faucet is turned on so you will be sure that the valves are holding. If they are not holding or you don't have them underneath you will need to shut off the water main. Keep the faucet in the warm setting and open when you turn off the main. Turn on any faucets that are higher than the one you are working on so they will allow air into the line and the water from the pipes above will drain from the faucet you are changing. Once all the water stops dripping you can change the faucet by unscrewing the hose from the faucet. The connections are behind the sink bowl. You will probably need to crawl in the cabinet a little and look up to see the connection point.
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Sorry, I misunderstood your question. Are you trying to disconnect the sprayer/faucet handle hose line to back wash it to remove the rust? If so, typically those have a quick release style connection. The connection happens underneath where I mentioned before. Sometimes the plastic at the connection gets slid back then the hoses pull apart, sometimes they have a turn style connector. You will need to climb underneath with a light and toy with the connection.
General C&ontractor
20 years exposure to the Home Improvement industry.