The phrase "to redeposit the miles" means taking back the airline miles that were previously used for a ticket or reward and putting them back into your account. Full definition
Business and first class awards will soon cost $ 300 for a no show / canceling within 24 hours PLUS an additional $ 75 to redeposit your miles back into your account. (travelcodex.com)
However, in eight years of planning vacations, I have had many leave periods changed or deployment dates changed, and I have never had no problem getting an airline to fully refund my ticket or redeposit my miles from an award ticket with no fee. (rewardexpert.com)
Korean Air does allows you to redeposit miles for free at any time and use them later on, so if I found availability on a nonstop flight, I could always cancel the original ticket and not lose any money or miles in the process. (thepointsguy.com)