delete an extra edge from BST

Given a BST, remove an extra edge to make it BST.

7

/ \

5   9

/  \ /

3    8

 public void deleteEdge(TreeNode root) {
     if(root == null) return;
     root = dfs(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
 }
 private TreeNode dfs(TreeNode root, int left, int right) {
     if(root == null) return null;
     if(root.val <= left || root.val >= right) return null;
     root.left = dfs(root.left, left, root.val);
     root.right = dfs(root.right, root.val, right);
     return root;
 }