Changing Addnl Data Tab text in ML81N

Hello all,

i have created an additional tab in ML81N, using screen exit - SRVEUSCR(

User screen on entry sheet tabstrip),

i tried to change standard tab name from Addnl Data to some customized name say MBOOK, following way,

on screen 399 goto->translation

but here after double clicking XMLU , i did not find any addnl data text where i could change to customized text,

please can any one suggest where i am going wrong,

thanks in advance..