Wodify will allow you to update a member's billing date without having to create a new membership.
Here's what you need to do:
1. Click into their current membership
2. From the "Actions" button, click on "Generate Next Membership"
3. You will be directed back into the membership page
4. Click into the newly created membership
5. Change the billing date under "Plan Details" and click "Save".
This will create a new prorated invoice.
For example, if the membership bills on the 1st of the month and you generate the next membership that will renew on 3/1 and change the billing to the 15th, Wodify will create a membership from the 3/1 to 3/15. On 3/15 the membership will fully renew for a month and begin to bill on the 15th going forward.