Final answer:
The corrected sentence should have the first word capitalized and a period to separate two distinct thoughts.
Step-by-step explanation:
The sentence provided by the student should be corrected for proper capitalization and punctuation as follows: "Darren told me that he doesn’t know when the party is. I will have to ring and find out later." This correction adds the necessary capital letters at the beginning of the sentences and inserts a full stop to separate the two complete thoughts.