I am first time growing tomatoes and seedlings were very good till yesterday. Seeding age was about 35 days ( from 5th December).

I am growing seedlings in the field under a plastic tunnel. However the tunnel structure was not very good, and there were patches on it where frost and water was accumulating over it. Yesterday there was a shower/rain in evening and then at night lot of frost and it was very cold. The water got accumulated over the plastic sheet over the seedlings ( tunnel height about 18 inches from the ground). At the night the water got frozen due to the cold and frost and in morning when I visited, there was ice cubes over the plastic sheet. I removed the water and ice, and tomato seedlings were looking a bit sick and leaves started dropping.

During day time it was sunny and heat build up under plastic sheet, when i checked the seedlings at noon those were rotting and leaves started to turn brown and burnt. :(

Till evening leaves of 90% of seedlings are damaged and only stem is remaining. Any advice what to do?