Grammar
그렇다면
if so / in that case
Form
그렇다 + -다면 — “if so”, “in that case”.
Function
Treats previously stated information as a premise for what follows.
Why this form?
그러면 — “then / in that case”: more direct transition; 그렇다면 highlights the premise as conditional.
Forms not to confuse
그러면
그러면 내일 봐요. — Then see you tomorrow.
Examples
그렇다면, 저희 모두가 기억이 없다는 게 확인됐네요. — In that case, it has been confirmed that we all have no memories.
그렇다면 다른 방법을 찾아야 해요. — If so, we need another approach.