Hello Ritesh,
ls_material is work area of internal table which is upload through excel.if u want pass the screen fields
in the FM "CONVERSION_EXIT_MATN1_INPUT" Just pass the screen fields value in new internal table .
under that loop use the FM and pass the work area values as input to the FM.
I hope this solve u r issue.
Regards,
Ameya Karadkhedkar