Helping breastfed baby take formula


So I’m a first time mom and my son is 10 1/2 months already 😭 he is a little underweight and doctor suggested to give him formula. So I tried enfamil gentle ease and he wouldn’t accept it. I mix it in cereal and he eats it no problem, but the bottle he won’t drink it. I also want to give him formula at night because he wakes up every 2 hours or sometimes every hour. Has anyone went through this and what helped your baby accept formula? I still plan on breastfeeding I just need the help 😅😅 thanks