Yes, admins can edit a submission on an applicant's behalf at any time, even after the submission deadline and in any status, including Accepted. Go to Data Management › Submissions, click the eye icon next to the submission, then click Edit in the top-right corner of the form and make your changes. How you save decides the status: Submit resubmits it, which can send the Thank You email again and set the status to Ready. Save & Logout saves without resubmitting, but moves the status to Incomplete, so set the status back afterwards if you need to.
This applies to event admins. To let the applicant make the changes themselves, see Admin - How do I let a submitter edit their submission?
Steps
Hover over Data Management (the clipboard icon) and select Submissions.
Click the eye icon next to the submission to open it.
Click Edit in the top-right corner of the form.
Change the answers you need to update.
Click Save & Logout to save without resubmitting. It logs you out of Reviewr and moves the submission's status to Incomplete. Only click Submit if you want the submission resubmitted.
To give the submission its previous status again, log back in, go to Data Management › Submissions, tick the submission and choose the status from Mark As in the bottom-left dropdown.
Important: Submit can send the submission's Thank You email again and sets the status to Ready. Save & Logout doesn't resubmit, but it sets the status to Incomplete. By default, Incomplete is an editable status (set under Configurations, on the Submission tab, as an Editable Submission Status), so the submitter can edit their submission again until you change the status. Check the status afterwards and change it with Mark As if needed.
Note: The submission's Activity Log tab records when someone, admin or submitter, clicks Save & Logout or Submit, but not which answers changed. The event's own activity log doesn't show edits to individual submissions. Keep your own record of what you changed if you need one.
If that didn't work
Required questions stop me moving through the form
When you edit a submission, clicking Next or Submit with a required question empty shows an error, for admins and submitters alike, even if the applicant left it blank. Save & Logout still works with required questions empty, so you can save the changes you've made so far. If you only need to add a document, upload it on the submission's Attachments tab with Upload Attachment instead of editing the form.
My changes don't show after I save
The submission list can show an older version until the page reloads. Log out of Reviewr and back in, then open the submission again from Data Management › Submissions.
The field I need to change isn't on the form when I click Edit
The Edit view only shows questions that are on the submission form. If the field you need isn't there, add it in the form editor or contact the Reviewr team through the in-app chat.
The status still says Ready after I used Save & Logout
Save & Logout moves the status to Incomplete, but the list can show the old status until the page reloads. Log out of Reviewr and back in, then check the status on Data Management › Submissions again. To set a different status, tick the submission and choose Mark As in the bottom-left dropdown: see Admin - Updating Submission Statuses.
I can't find a Save & Logout button
The button is a form question of the Save and Logout type, and admins can change the text it shows in the question's Title field, so it may have a different label on your form. If your form has no such button, add a Save and Logout question in the form editor.