The reversal of the letters b and d are fairly common and nothing to worry about until about 3rd grade when the brain becomes hard wired.

Here are several ways to help your student remember the directionality:

• Remember the word bed, which is in the shape of a bed. /b/ at the head board and first and /d/ at the foot or last.
• You can take an approach of finding “something” that the letter roundness points to in the learning space relative to the student desk, such as “the letter b points to our window—the bees(b) are outside, or the letter d roundness points to the door, (dad is at the door) that word starts with /d/. 
• Have a reference letter band your student can refer to.
• For younger students—have them repeatedly practice sky tracing imaginary huge letters using gross muscle movement; standing with pointed finger and a locked arm like a soldier. Guide the direction of the forearm with your hand and then fade. This helps to recall directionality relative to their bodies. Eventually bring the tracing down to smaller and smaller tracing or writing.