Introducing hungry baby milk

i am looking advice as to how to introduce hungry baby milk to my baby. He’s 3 weeks old, over 10lb weight and drinking less than every 3 hours. 

I wang advice as to how to introduce hungry baby milk. He doesn’t seem to settle on the ordinary. He’s on aptamil number 1. 

at what time of the day should I introduce it? How many feeds a day initially? And should I add another ounce of water in when making it?

any advice would be much appreciated thank you