So, you didn’t exactly get to protecting your plants when the frost came–for whatever reason–and they’re now drooping and brown. It happens to all of us. Just last year we lost most of our tomato harvest to an early frost and they were ready for harvest! Never again.
Anyway, most of your plants will come back from a hard frost, as long as they have not been completely killed. When “real” Spring comes along, with no danger of frost, clip back the damaged parts so they don’t spread. At the same time as making the plants prettier, this move will encourage new growth.
Fertilize them as well with a balanced fertilizer (with equal parts nitrogen, phosphorus, and potassium). This will also encourage strong growth. Make sure you follow the directions on the package for best results.
If you plant was really tender, dig it up and take it to a greenhouse. Often, with a little heat and moisture the plant will revive in no time. This would be a last resort, but one that you can reserve for a very special plant.
Other than the above, there’s not all much more you can do to an injured plant–just care for it and hope for the best!