How to apply Patch for updating party_name in GL entry?

I have a created custom field party_name in gl_entry and also written code in patch to update party_name in GL Entry from customer(party in gl_entry) .But its not working …
Can anyone helpme ??? How to write a sample code for updating value to field .

Try this
cur_frm.add_fetch('*Source field name*', '*Source*','*Target*');

Thank u @rk_root i will check.

Try this
cur_frm.add_fetch(‘Source field name’, ‘Source’,‘Target’);

It is also not working.