Much like in the case of builtin lists, you'll just be working with builtin functions (or rather, Plutarch synonyms to builtin functions) here. You can find everything about that in builtin-pairs. Feel free to only read the Plutarch examples.
In particular, you can deconstruct PBuiltinPair using pfstBuiltin and psndBuiltin. You can build PBuiltinPair (PAsData a) (PAsData b) terms with ppairDataBuiltin:
ppairDataBuiltin :: Term s (PAsData a :--> PAsData b :--> PBuiltinPair (PAsData a) (PAsData b))It's also helpful to note that PAsData (PBuiltinPair (PAsData a) (PAsData b)) and PAsData (PTuple a b) actually have the same representation under the hood. See PTuple