I should have used the word “participating at Mass” rather than “Assisting”. I have read guidelines that used the word “assisting” to mean “participating”, as in laity sitting in the pew responding and praying along with the Mass and so forth, but someone always gets confused thinking “Assists” means you need to be the altar server or the deacon or the lector etc, which is not necessary. Actually, I can see “participating” being misinterpreted the same way.
Anyway bottom line is that as someone else said, in order to receive a second time you need to attend a Mass and do the things the congregation normally does like respond at the proper points, pray the communal prayers, listen to the readings, etc.