Welcome to the Community, @keeliaboutique.
I'll be happy to share with you the steps on how to clear your browser's cache due to the unexpected behavior that you encounter while adding a new customer contact.
Let us also try accessing your account and add new customer contact using a private browser or incognito browser.
Here are the shortcut keys that you can use:
Please also try to zoom in and zoom out your browser, it can be that the Button is hidden due to having a small screen.
Lastly, to check any issues with your browser’s health and its compatibility with QuickBooks Online, you can also use the Browser Health Checkup Tool.
I'll be here if you have other questions about adding new customer contact. Let me know in the comment section. Have a great day.