Customize newsletters in html code - max 1 hour work

hello, I need to change html code of the newsletters in a shopify app Rise.ai - (Formerly GiftWizard)

Change the newsletter colors
Use your own branding/logo
Center align the text
Use the Lato font
Color the buttons black

There are three - four newsletters to change
I think those are three. I am not sure if there is also a reminder email programmed somewhere in the app (in case person does not use up the card for some time)

1. BUYER NAME bought you a gift card at Appareal
2. Confirmation for Gift Card order BUYER NAME
3. Update about your gift from Appareal
4. Reminder of an unused card (I am not sure if there is a newsletter like this but I assume there is)

Thank you!