Welcome to the Amplitude error detection beta. To merge properties, first go to the advanced tab - you can get there by clicking the link in the email we sent, or by going to "manage data," selecting the project you want to delete events from, and clicking "advanced" on the left sidebar. Then you will need to select either the "User Properties" tab or the "Event Properties" tab (depending on which kind of properties you want to merge).
Now click the "transform button.
Next, select the properties you want to merge, and click the "merge" button. The merge dialog will appear. Enter the name of the merged property and click "next."
Finally, click the "merge" button. You will be in transformation draft mode, and can test the merge before publishing it. To publish, click the "publish" button.