If it was my date or girlfriend I’d just break up with them. At that early point in the relationship it’s not worth the effort to try to change their mind, because this difference in opinion is likely indicative of a larger set of different values which indicates that the relationship wouldn’t work out long term.
If my wife suddenly came out as homophobic, I’d just take her to the doctor to check for brain problems. Going from bisexual to homophobic is quite odd.