There are two aspects that you can customise on the notecards: a logo + a footer.
Your logo can be sized and positioned as you wish. Make sure you’ve got a high-resolution JPEG or PNG file of the logo you wish to use.
Insert any text you like, in the font and colour you wish. Have a think about what you want to go in the footer of your message. Maybe it’s some text about your business or a lasting message, or something simple like your social media handles or contact details.