I highly recommend All About Spelling. It’s a homeschool curriculum and it is amazing. My third grader struggles with spelling and has improved so much. It’s about 15 minutes a lesson. I do it right after dinner about 3 to 4 times a week. What’s amazing about this program is that it gives kids spelling rules - my daughter was just not picking up the patterns on her own and the way spelling is taught in schools really does not help someone who just doesn’t get. For instance we both learned this rule:
Floss rule: When a one-syllable words ends in f, l, or s, double the final f, l, or s (mall, off, etc.)
Start with level 1 which is basic but will provide a nice foundation.