API Request to Update Single Field via http functions

Got it to work by getting on the right track with the suggestions of @russian-dima . The solution was a combination of that as well as using toUpdate:

export function post_codeWorks(request) {
 let options = {
 "headers": {
 "Content-Type": "application/json"
        }
    };
 // get the request body
 return request.body.json()
    .then((body) => {
 return updateProfile(body["_id"], body["qrCode"]);
    })
    .then((results) => {
        options.body = {
 "inserted": results
        };
 return created(options);
    })
 // something went wrong
    .catch((error) => {
        options.body = {
 "error": error
        };
 return serverError(options);
    });
}

async function updateProfile(profileId, qrCode) {
  wixData.get("memberRegistration", profileId)
    .then((toUpdate) => {
   toUpdate.qrCode = qrCode;
   wixData.update("memberRegistration", toUpdate)
   .then((result) => {
 // updated object details
      console.log(result);
   })
   .catch((err) => {
 let errorMsg = err;
   });
})
}