How to switch to free version after the end of trial?

How to switch to free version after the end of trial?

Hi, we are using Zoho Desk with Zoho Assist. Now the trial period finished and we're not able to continue using the Zoho Assist. We are being shown the message:

Your 15-day free trial has expired.
Contact your Organization administrator to proceed

What should we do to continue using the free version?

Thanks,