Form 12b to be procured from previous or current employer

Dear Sirs,

                  Kindly suggest as to whether a salaried employee who has undergone a change in employment should

                 1) Submit the "FORM 12B" to his Previous Employer or Current Employer ?

                 2) From where/whom shall such "FORM 12B" be obtained ?

                 3) In case he had not provided HRA Payment details to his Previous employer earlier can he provide it now ?

                 Kindly reply at the earliest

Thanks