Ragic has a built-in reminder system that can be triggered by the values entered in the date fields in your sheet. This reminder system can send out e-mails automatically according to the amount of days you set, before or after the date.
If you want to receive reminder e-mails on a certain day of the week instead, you can use a simple formula that will calculate this day of the week first, and set this date to send out reminders.
The following formula example will calculate the date of the next Sunday, and send reminders on the next Sunday for a date in field A1.
A1+8-WEEKDAY(A1)