To add dialog fields and get run time lookup on the dialog field in AX 2012 SSRS reports You can get details on following link.
Dialog fields and runtime lookups on SSRS Report parameters
You can get some other good link for SSRS report in ax 2012 on above link.
Dialog fields and runtime lookups on SSRS Report parameters
You can get some other good link for SSRS report in ax 2012 on above link.