There are two problems, bringing it to the center and the main problem is it is been throwing purple fireball so i can not even stay at the bed killing area (yea ik my eng is so bad sorry)

Since the Ender Dragon only throw breath where the player is, during One Cycle, we basically wait around the pillars until the Ender Dragon descends to the center. If the dragon throws a breath, we just walk a few blocks to avoid it. This saves time you wait for dragon too.

Keep moving to avoid the fireballs and the lingering cloud of Dragon’s Breath. Attack the Ender Dragon with bows or crossbows from a distance. If you have empty glass bottles, you can collect the Dragon’s Breath to use in potion-making. Hope it may help you!