Hi @ramesh12345
Try this
| makeresults
| eval str="Test-20190212-0912"
| rex field=str "-(?P<year>\d{4})(?P<month>\d{2})(?P<date>\d{2})"
| eval result= year."-".month."-".date
Use a rex first and to split the parts of it and then concatenate it to your new field
| makeresults | eval time="Test-20190212-0912" | rex field=time "Test-(?<year>\d{4})(?<month>\d{2})(?<day>\d{2})"
| eval time=year+"-"+month+"-"+day