You can upload an activity to the Strava iOS app even if wasn't recorded with GPS
To enter a manual activity, select the plus sign icon on the top left of your feed (highlighted below.) Choose the Manual Activity option.
From the manual activity edit screen, you can enter your time, distance, and speed. Add a photo, select your activity type and a tag. Finally, set your start time, attach gear if applicable and add a description. Once you save the activity it will be uploaded to your Strava account.