Note: This is general advice; please make sure to talk to your child's teacher and/or your pediatrician if you have any specific concerns.
Capital letters backwards is very common at that age. From Dyslexia.org:
The majority of kids outgrow reversing as they get stronger at reading and writing. Reversing letters is typical and fairly common up until second grade.
That’s because the letters b, d, p, and q are really all the same letter. They’re just flipped and turned. As adults and experienced readers, we’ve learned that their position makes a big difference.
Young kids and beginning readers don’t always make that distinction right away, though. That discovery is part of the learning process. It comes as kids build their skills and become more experienced readers and writers.
They also have some great advice for how to help your child learn their letters:
How can I help my child at home with letter reversals?
Work on one letter at a time. For example, if your child is reversing b and d, start with b. Don’t introduce d until your child is having much less difficulty with b. After that, you can work on other significant reversals, such as p or q.
Do the same with numbers. Work on only one at a time. When your child is having much less trouble with that number, you can move on to the next.
Additionally to the sourced information, my personal experience is that 5-6 is still very common to have some letters/numbers backwards, and to have some trouble with left and right as well. Both of my children, who are very strong and early readers, continued to get the common letters and numerals backwards at 5.
My youngest is 7 and still has some trouble with a few numerals, though not so much we're concerned - they are able to do the numerals properly when they think about it, they just don't take care to write them properly right now. We're going to spend the summer working on the individual numerals. We've addressed this primarily by talking with their teacher and pediatrician, both of whom are comfortable with where my youngest is right now. I think the most important thing is to keep asking these two professionals on a regular basis to ensure we are aware if it moves to the "problem" category.
When we work on writing or math, per instructions from the teacher we are very careful to separate whether we are teaching "math" or teaching "handwriting"; when we are teaching subtraction, for example, we don't correct backwards numerals, and the same with when we are teaching writing - if they are answering a question about a passage they read, we focus on a good answer rather than correctly formed letters. Handwriting is a separate skill, and something that needs to be focused on by itself to avoid frustration spilling over and making the activity too difficult or too frustrating.