Thanks for posting your question in the Apple Support Community. I understand that your contact card is changing back to an incorrect address after you change it.
If you haven't already, I recommend to force close the contacts app, then restart your iPhone and check to see if the card is still changing to the wrong information.
Force an app to close on your iPhone, iPad, or iPod touch
Restart your iPhone, iPad, or iPod touch
If the contact card is still displaying the wrong information, I recommend to try completely deleting your contact card then add it back. You can delete it like any regular contact by going to Contacts > tap your name > tap Edit at the top right > tap Delete Contact at the bottom.
Let me know if you're still having trouble after going through these steps.