Take bracket off bend it the opposite way and bolt it back down, or buy the correct battery. I have owned many different types of cars and trucks and I don't think any of them had a tie down and I have been fine all these years lol.
Looks to me like they sold you an undersized battery. Either return it for the correct battery, or get an adapter plate and put it underneath it. You can see it in this picture:
I just saw that pic. That battery is definitely the wrong battery. The threaded post on the left side is to tighten down your hold down. Its maxed out because your battery is too small. Either that, or you're missing a mount underneath it.
Fortunately-your positive is covered so no fire stsrts-but you can still mess up your plates inside.