Hey, I thought my 4/5 month old would never learn to take the bottle. He's been exclusively breastfed and would always scream his head off in protest if I tried him on a bottle. I'm still breastfeeding but I just wanted the option of having a few hours away from him if I wanted or god forbid have an evening out! After a bit of trial an error he will now happily take a bottle. Here are my tips that worked for me:
-try to find the right bottle and teat for him/her. There are so many on the market but I was lucky to be given a load of different bottles from friends that I could try. Each baby is different but mine liked teats that were rounded like the Dr Browns teats and Avent. So it may take a few tries with different bottles.
-try him on a bottle when he is calm, happy and not hungry. I'd often give him a feed and then wait an hour or so and then try him on a bottle. It was less about giving him a feed and more about getting him used to the sensation of a different kind of teat and different way of being held.
-It may take a bit if time, I think it took me about a week (maybe less) of trying him with a bottle just once a day and don't force him to take a bottle. If they seem uninterested or protest just put the bottle down and try again the following day. The main thing is for them to understand that milk can come from other places other than the breast.
-I found putting a bit of breastmilk on the end of the teat helped.
-Also, I would express some milk and then feed it to him immediately so it was fresh and at the right temperature so that it's familiar to them. You only need to do this at the beginning, my baby took cold milk the other day.
-get someone else to feed them the bottle, preferably the person who'll be feeding them when you're away. If they're with you they'll expect the breast.
I was convinced my baby would never take a bottle, but it just takes a little patience and perseverance and they'll get it in the end. I can now get others to feed with a bottle or do it myself. Admittedly night feeding is still a little tricky as he wants the comfort of the breast, he'll guzzle the milk but stay wide awake for the poor person who's looking after him!
Good Luck!