How are symplectic forms used in string theory?

Question

Sämann and Szabo in "Groupoids, Loop Spaces and Quantization of 2-Plectic Manifolds" (https://arxiv.org/pdf/1211.0395.pdf) show that one can transgress a 2-plectic form on some manifold to a symplectic form on the knot space, which is (a restriction of) "the configuration space of a bosonic string sigma-model on $S^1 \times \mathbb{R}$ with target space $M$."

Szabo in another article (https://arxiv.org/pdf/1903.05673.pdf) writes that "In higher geometry it is well-known that the nonassociativity features of a gerbe on M can be traded for more conventional noncommutative features of a line bundle on the loop space... [the mapping] has a natural interpretation of trading particle degrees of freedom for closed string degrees of freedom"

I have no background in string theory, so I am not sure how transgression techniques are used from a physics standpoint: When one transgresses a 2-plectic (or n-plectic) form to a symplectic (or (n-1)-plectic) form on loop/knot space, what significance does the latter form have in string theory? How is it used?

Any references on the topic are welcome.