Explanation:

- Original sentence: "Thank you all for coming so earlier at the morning."

- The phrase "earlier at the" is incorrect. "Earlier" is a comparative adjective, typically used to compare two specific timeframes, requiring rephrasing.

- Option 1: "the early in a"

- Incorrect. This introduces an awkward structure. "Early" is not used correctly here.

- Option 2: "early in the"

- Correct. The phrase "early in the morning" is a standard, grammatically correct expression.

- Option 3: No improvement required

- Incorrect. The original phrasing is awkward and ungrammatical, requiring correction.

- Option 4: "earliest on the"

- Incorrect. "Earliest" is a superlative, not suitable here, and "on the" is awkward.