You have two options, either add a zprs_offshore description field (Character field withe required length) in ty_tab. And modify the table to update the table it_itab.
types: begin of ty_tab.
...
...
..
offsh_desc type char10 ,
...
end of ty_tab.
lv_ofsdesc type char10.
loop at it_itab into wa_itab.
" Use the above code to get the description in lv_ofsdesc = it_taba-domvalue_l.
perform get_domain.
wa_itab-offsh_desc = lv_ofsdesc.
modify it_itab from wa_itab index sy-tabix transport offsh_desc.
endloop.
Now you can use the field wa_itab-offsh_desc in your smartform.
Another option would be to call the above FM within the loop in the smartform. And providing the variable having the output in the smartform.