If you didn't receive a verification email after signing up, you can resend it anytime from your profile on the Web app: https://app.zeplin.io/profile
A verification email should normally arrive pretty quickly, but occasionally it might take up to an hour. In the meantime, you can keep using the app without any limitations.
If you still didn't receive the email, make sure that you've typed your email correctly while signing up and check your junk/spam folders.
For corporate email servers, Zeplin's emails might be blocked by default until they're whitelisted, make sure to contact your IT team to check if that's the case.