changing the field of an internal table

Hello All,

I am working on a requirement, where there a table declared as below:

t_data type lfa1.

this table has some data in it, now I need to change only one field of t_data based on some validation. I tried teh following approach but it didn't work:

it_data = t_data.

read table it_data into wa_data with key lifnr = '100100'.

if sy-subrc = 0.

wa_data-nam1 = 'TEST'.

append wa_data to it_data.

t_data = it_data.

but when i executed the above code I am getting the error message... can anyone please help me with this.

Thank you.