I clean my baby’s neck more thoroughly when showering so as to get rid of the saliva/milk trapped at her neck. Throughout the day I also try to wipe it clean and I apply this AFA multipurpose baby balm on her when I see red spots or areas. Usually goes away the next day :) https://s.shopee.sg/4AgXNOT1m1 this one!
Try Sudocrem! It works well for my bb for drool and heat rash.