This is from TDA, so I think you go through your broker:

"Please note: Warrants may be extended, amended, or withdrawn by the issuer. TD Ameritrade charges a voluntary tender offer reorganization fee to submit your warrant exercise instructions, and we request that we receive your instructions at least 3 business days prior to the expiration date to ensure that the agent will still accept your instructions. If your instructions are received less than three business days prior to the expiration of the warrants, we will process on a best-effort basis only."