If you see your activity on Strava with the wrong date, it is most likely a recording error of the device you are using to record GPS. A GPS file is composed of location coordinates and timestamps where each coordinate occurs. Strava simply reads the earliest timestamp in the file that is uploaded to Strava and displays it as the start time on the activity page.
For example, if there is an error in the beginning of the activity file where a device incorrectly records a date far in the past (1980 for example) then Strava will display the ride as starting in the year 1980 even if the remaining timestamps are correct.
If the device records all time data as occurring on an incorrect day or incorrect year (like far in the future as can happen with Garmin devices) then Strava will display the activity on that date and year. More about Garmin devices and bad time data.
1. If you're using a GARMIN device:
There's a useful third party site that you can use to adjust the date of a Garmin activity. First, you can get the FIT file from the device's internal storage or export the FIT file from Garmin Connect.
Once you're done exporting, use this site to adjust the date.
You'll need to delete the existing activity on Strava before uploading the fixed file (This will cause you to lose all kudos and comments on that activity).
2. If your GARMIN device doesn't have FIT files, you can export the GPX file from Strava, open the file in a text editor, and replace all the incorrect dates with the correct dates, then re-upload to Strava, per above.
3. If you're recording with the Strava mobile app, check that you have the phone's clock set to update automatically. The issue is most likely caused by two primary issues: Either the phone's clock is set to an incorrect time, causing the Strava app to record the incorrect time data, or the phone's software malfunctions and records just one (or a few) timestamps that are incorrect, either way in the past or way in the future (this happens mainly with Android devices).
To fix this, you can try #2 above, or you can try using the crop tool on the website to trim just the very first or last points which is often where the bad time data is found.
If you're still having trouble, don't hesitate to reach out to us directly.