const batchArray = []
var index = 0
docArray.forEach(ar => ar.forEach(doc => {
   if (index%500 === 0) {
      batchArray.push(db.batch())
   }
   batchArray[batchArray.length-1].update(doc.ref, {app: app})
   index++
}))
batchArray.forEach(async batch => await batch.commit())