My parents are on B2 visa. They were visiting me and were supposed to leave USA on April 5 (their visa April 9). Due to Covid-19 situation, their flight got cancelled. We moved their flight to July 5 and applied for a visa extension till July 9. Their visa extension case is still under review. Now it seems like their July 5th flight will also get cancelled. How can we request for further extension on their visa extension application? Can we send a letter or amendment? Or do we have to file another new application? Please advise.