Since one is scared of the other, youll need to keep them completely apart for about a month. Completely apart meaning different rooms for each bunny so they cannot see or smell one another for a full month.
After this month, youll have to do prebonding . Prebonding is when you have their cages next to eachother, but about 10 inches apart so they can see and smell one another, but cannot reach. Youll have them in this set up for another month. After this month (now two months in), youll start swapping them between cages. So every even night, bunny1 is in cage1 and bunny2 is in cage2; every odd night, bunny1 is in cage2 and bunny2 is in cage1. Youll do this swapping for a month or two.
After the prebonding stage (now three to four months in), you can begin bonding. Bonding has to be done in a room that neither bunny has been in before. Youll start with multiple short sessions per day and slowly increase their time together in this space so long as they are not aggressive. Youll continue bonding daily or almost daily until they can go up to 4+ hours together without any aggression in that neutral space.
After the neutral space bonding, youll start the same bonding tactics in their future shared space. Again, youll start with multiple short sessions and slowly escalate over time until they can now spend 8+ hours together without any aggression. At that point, you will want to do a 48 hour trial where you sleep outside of their shared cage and stay with them the full 48 hours. If there is absolutely no aggression during this time, you can likely consider them bonded.