Change the Monthly Gift Date
As there isn't a way to edit a subscription date once the initial date has been set (ex: change from the 15th of the month to the 1st), you'll need to first cancel your current subscription, then create a new monthly subscription on the date you want your subscription to be charged.
Log in to your personal Donor Dashboard (found through any of the Harness fundraising pages or the email receipts you've received)
Select the person icon in the upper right-hand corner
Select "Monthly Gifts" from the drop-down menu
Identify your monthly subscription & select the 3 dots to the right of it
Select "Cancel Donation"
*Do this part on the date you want the monthly gift to charge.
Select the person icon from the upper right-hand corner
Select "Monthly Gifts"
Under the section titled "Monthly Donations", set your donation amount
Select "Give Monthly"
Confirm your payment source (card on file or other), cover fee, whether/not to leave note or make gift in honor/memory