There is no way to downgrade a subscription, only upgrade.  You will have to cancel your current subscription and start all over with a new one.

Resolution for 'basic small issue: 'I am trying to change my subscription. I cannot see how I can change from QB Plus to the basic small business version.' available: Yes.

The basic small issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the basic small issue yourself by looking for a resolution described in the article. If it is a complex basic small issue or you are unable to solve the issue, you may contact us by clicking here or by using other basic small support options.

For more information about resolving issues related to basic small in Quickbooks/QBO or to get support for the issue 'I am trying to change my subscription. I cannot see how I can change from QB Plus to the basic small business version.', click the link below: