Girls, son is 2.5 months old. Previously there was plenty of milk and…

Girls, son is 2.5 months old. Previously there was plenty of milk and I could pump without problems if I had to leave somewhere and the baby stayed with dad. Now there's less milk and it's not possible to express anymore, but the baby eats well and gains weight well. It was decided to introduce formula only when I need to be away for more than three hours. Bought Nan Supreme formula, mixed 30 ml today for a trial, the son had an allergy. How can I then introduce it so that it can be given 1-2 times a week?