DiscoTOC is a theme component not a plugin. It is installed following How do I install a Theme or Theme Component? and it is definetly available for you, give it a try.
Oh I see.
I think trying to get a working repl.it instance for prolog, even if powered by SWI-Prolog compiled to WASM may be your best bet. Try contacting the repl.it founder @Amjad_Masad .