After I have tested the form how do I remove the test submissions?

In order to remove the test submissions you submitted when you were trying out your form you would need to view your submissions from the my forms page by selecting the form then clicking the submissions button at the top of the forms listing.

Once you are viewing the submissions simply select the submission and click the trashcan or red x to delete the selected submission. You can also use the "delete all" function if you have multiple submissions. See screenshot below.

Also, please note that deleting your submissions does not change your plan's monthly submission usage as in if you submit 1 submission via your form for a free account as an example it would still stay at 1 out of 100 for the month even if deleted until the monthly reset occurs.