Haven assess and approve all applications on a variable rate. There is no issue with changing to a fixed rate for your loan offer - you would just need to complete their fixed rate application form (if you did not specify a fixed rate at the time of the original application), which your broker can provide to you.
Haven's rates = AIB's rates. EBS split away some time ago to offer 2% cash back, and now they have lower fixed rates, but their variable rates are higher than those of AIB/Haven.
Best regards,
Dave Curry CFP®
https://www.linkedin.com/in/davecurryirl