Student or Learner
How can the sentence below be rephrased to a formal sentence.
Or is it formal enough?
"We support the detailed explanation written in our previous letter."
I would remove "written" (or change it to "given") and leave the rest alone. "We support the detailed explanation [given] in our previous letter" seems formal enough to me.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.