Yes, you can edit the survey after completing the data collection. Please refer to this Knowledge base article: Edits to an Existing Survey123 Form that Do Not Delete Feature Layer Data.
You can also edit the data that has been already collected using Survey 123. You can go to the same survey Using the survey 123 app and click the ‘Send’ tab and click the specific survey response and start editing and then finally send it again. The responses will automatically be updated inside the feature layer. You can also access the feature layer and edit the responses from the survey by using the Cadasta Platform – AGOL.