LLC is not a business type

How you will be taxed as a new business is the key,  sole proprietor, partnership ??

see this for whether or not you are allowed to keep the EIN

https://www.irs.gov/businesses/small-businesses-self-employed/do-you-need-a-new-ein

Resolution for 'Corp to LLC issue: 'Conversion from Corp to LLC' available: Yes.

The Corp to LLC 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 Corp to LLC issue yourself by looking for a resolution described in the article. If it is a complex Corp to LLC issue or you are unable to solve the issue, you may contact us by clicking here or by using other Corp to LLC support options.

For more information about resolving issues related to Corp to LLC in Quickbooks/QBO or to get support for the issue 'Conversion from Corp to LLC', click the link below: