An interesting challenge, Elle.
That you recognise the shortcomings of your earlier efforts indicates how far you have come as a writer. That you feel those existing stories are somehow sacrosanct suggests you still have a way to go; one price of a pantser approach is that major reworking is de rigueur.
One way to approach this, if you want to resurrect one of the old projects, would be to read through it, then put it aside, and plan out a rewrite. Not as the same book, per se – give it a different title to help dissociate them – but as a derived project. Write the replacement without referring back to the original.
Of course, there is a caveat on this: do the ideas underlying those projects still hold your attention as they did when you first worked on them? Or are you trying to revive them so that they don't feel like wasted effort? (They're not wasted. They were learning exercises.)
Whatever you choose to work on next, it should be a project that engages your emotions.