Breastfeed to formula milk

Hey guys, I've been breastfeeding my baby for almost 5 months now. Since I'm working it's hard for me to stock up milk for him. So i started to give formula milk for him. He was okay with it for a week. But now he don't wanna drink the formula milk at all unless it is mixed up with my own breast milk. How can I practice my baby to just drink formula milk without depending on my milk? #bantusharing #firsttimemom #firstbaby #advicepls