I had terrible problems getting my dd to take expressed milk from a bottle, nearly gave up, but was returning to work so the pressure was on - here's what I did.
We first gave dd a bottle of expressed milk at about 10 weeks - she took it beautifully, so we thought that's that and didn't bother again for a month or so. From 4 months on she just wouldn't have anything to do with it - screaming, wriggling in arms etc. So ....
From about the age of 4 1/2 months, I introduced a daily bottle session. I chose the 10:30am feed (having last fed at 7am, and having just woken from a nap - so calm but hungry). I would put on the same soothing music and walk her up and down the room with the bottle in her mouth. When she got upset I'd cuddle her and get her calm and then stick the bottle in and try again. Keeping walking seemed the best way of keeping her calm. She didn't suck at all for a couple of weeks, then gradually would take 1/2 oz but no more for another week. Then suddenly one day she drank 3 oz, another few days of messing about and then about 3-4 weeks after the new daily regime she started taking the milk successfully all the time.
When she failed to take the milk initially, I would stop trying after about 10-20 minutes. Give her a break by playing with some toys for quarter of an hour and then breastfed her. I resisted feeding her immediately after failing with the bottle, as I didn't want her to think "if I don't take the bottle, I'll get the breast". Not sure how clever babies are, but you never know
I kept up practise sessions with the bottle every other day until she went to nursery 3 days a week at 6 months.
Also I used the No 3 (fast flow) avent teats, where the milk drips out a bit into their mouth, as opposed to the slow flow ones where you have to suck to get anything at all. The milk dripping into dds mouth seemed to give her the idea of sucking!
Good luck. You can do it - if you're stubborn enough!