To do so, go to Brand Settings -> the Task tab -> the Housekeeping card and turn off the toggle of Auto-approval. This way, you can manually Approve or Reopen the task completed once submitted by your housekeepers. You can also turn on the toggle of Mandatory Housekeeping Photos to request housekeepers to take at least one photo of every room before being able to submit a cleaning task.
Then, go to the Task dashboard and click on your desired Pending task. On the opened page, you can click on Approve or Reopen the task after viewing the images.
Note that after approval, the status gets Completed and you will not be able to make any changes.