I assume you are not able to login on a published application. A local application has user ID MxAdmin and password 1. This will not work on the Mendix Cloud. You could have created an Administrator equivalent user and a Snapshot of the data. This would have provisioned that data to the Cloud on the initial built.
Now you can use an after-startup Microflow that retrieves a specific Administration.Account with a known name. If not present, you can create it with a hardcoded password in the Microflow.
Something like this:
Go Make It