Go through the word mat with your child and read the words with them.
Help your child construct their first sentence as some children find it hard to get going.
Encourage them to say their sentences aloud before writing and using their phonics to help them spell.
Your child should be able to write their own version of the story but may need some support to keep going.
Spelling doesn't have to be perfect just remind them to make sensible attempts. There should be some capital letters and full stops.