It actually sat in a freezing warehouse for 5 days because of a blizzard

What are the best root tabs to use and how do they work?
Ah yeah, that'll kill most plants, for sure! Sorry, I wouldn't even bother trying to save the roots then - see how they look when you're cutting the leaves... brown and rotting needs to come out. Rotting matter in a tank is never good!
I can't help with root tab brands I'm afraid, not in the US. But stick to known brand names, not random cheap stuff online. I bought some cheap Chinese root tabs from Amazon once, and they spiked my nitrites super high for two weeks, requiring daily water changes and me having to dig them out from under the plants. Not recommended!
All root tabs do is provide nutrients for the plants, since there aren't any in sand or gravel. Some plants take their nutrients through their leaves/the water column, and can benefit from liquid fertilisers (aquarium specific, not your general houseplant ferts!) and some feed primarily through their roots, so thrive better when given root tabs. Vallis, cryptocorynes, and amazon swords are pretty common plants to have, and all greedy root feeders.
Best to buy live plants seasonally when you can, when the weather is mild-warm, not in the midst of summer or winter. If you need plants in those times, better to try to find a local hobbyist selling trimmings from their tank, so you can pick them and get them home quick!