how do you prune Solanum and do they recoup from frost?

I Would not like to say as your levels of frost are far harder than ours. Over here we would remove any frost damaged branches in April and hope for the best. It is very vigorous when it gets going. It has 2 chances Live or Die!!

Which Solanum is it? S. crispum or S. laxum? Both are not happy with very cold weather, and can suffer - the S. laxum being more prone to die-back than the other. Yes, cut it back to healthy wood and give it a feed! Good luck.