Ah, Autumn Bonfire. They advertise thee to be hardy to zone 6 or 7. These cultivar have these short patent names like 'robleza' as well. Don't know why that is. This one should be hardy in zone 6, as an established garden plant. But it being a bonsai eventually removes 1 or 1.5 zones, maybe. So it will be hardy to zone 7 or 8 in a bonsai pot. But that is kind of speculation.
Most people do trunk chops on nursery azalea. See the azalea contest boards for many examples. This is two (or three?) plants sharing a pot (and their rootball) together. Separating them is quite invasive as you will have to cut the rootball in half so both plants will lose half their roots completely. So often it is safest to sacrifice one trunk. Or you can keep the two tree design.
It is kind of late to do a chop. If you do it now, it will still bud exactly the same way. But there will be less time for that growth to elongate and mature before the end of the growing season.
You can also go in now and prune back every branch that creates reverse taper. So that means that when you have several branches at the same trunk height, you remove all but one. And if the trunk has movement, you keep the one that is on the outside of that trunk curve. You don't need to prune them away completely. That can be done later. You can cut back hard these branches that you don't want to get larger, because they will be removed eventually. They will back bud and they won't negatively affect your trunk structure and your taper
I recommend the gradual pruning them back and growing in the full ground for a couple of years for azalea. That way, you can thicken up some branches and create a better tapering trunk than what you have on a nursery plant. Takes some time, though.
