Yes, open the ride from the map. Click on one of the lines and the activity name will pop up, click on that and Veloviewer will open the ride, as it does it recalculates the GPS points more accurately. Be careful though as you can lose squares as well as gain them.
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Thanks. I've just done it for a 300km Adax I did in 2013 which has corrected the 2 tiles I was looking at - but has also taken one tile off me - reducing my Squares from 40 to 39. Oh well, I'd rather have it correct. Will have to go get that one tile soon