It is not currently possible to manage multiple surveys from the Sent box at once. Can you please provide an example of the workflow that would benefit from this functionality? Usually, when resending survey from the Sent folder, it would be to edit an individual survey and resend.
We were hoping for this function due to an issue with an initial survey we created. We first collected 140 surveys, uploaded/synced the data to survey123.arcgis.com, and then exported the data to an excel file for back up. I then had to change a field type in the survey form, which required me to re-publish the survey, thus overwriting any data that was online. However, on our mobile device within the survey, we can still see that the there are "140 sent surveys", which no longer appear online because we had to republish the survey online thus deleting all of the records stored online. So, as we continue collecting data, it would be helpful to be able to resend these 140 surveys along with the newly collected data so that they all end up within the same table when we export the data to excel.
If you have changed an existing field type which caused republishing, you will not be able to send the existing surveys in the Sent folder to the new survey as the original feature service will have been deleted and a new one created in it's place with the updated schema. In the future, one option would be to export the data to a file geodatabase (prior to overwriting). After exporting, it would be possible to use a field calculation on the dataset to transfer data from one field type to another, and then append that data to the newly created feature service and survey. Have you attempted to submit one record from the Sent box at this point, and if so, what were your results?