It’s easy to check for alignment since some smiths index the top of block with the upper instead of the barrel port.
Remove the two bottom allen screws on the bottom of the block, then pull the gas block straight off the barrel. Do not twist the block or you will bend the gas tube.
Once the gas block is off the barrel, mic the center of the barrel gas port from the barrel step, then the distance from the back face of the block to the center of the gas block port hole. You do this to figure out if the block need be off the barrel shoulder to center up the ports or if it needs to be flushed.
The next item is pencil to line mark the barrel port down the top of the barrel forward past the port so you can index the gas block in this plane as well when you reinstall the block. You shouldn’t need to mark the block, just use the gas tube as a reference of the block port.
Once the block is in both correct index positions on the barrel, apply a thin coat of blue loctite on the screws and tighten them down to re-secure the block to the barrel.
Note: Since you have the screws out of the block, may as well check to make sure that the gas tube hole is aligned with the gas block port. If needed, chuck the block in a press with the gas tube still attached, and drill out any portion of the gas tube that is blocking the port. The treads are larger than the port passage, so if you chuck up true, you will be able to remove the overlap without touching the set screw threads (remember to set the press stop to keep from over drilling and punching threw the other side of the gas tube).