Verry easy and straight forward !
Just go to online matches and pick endless battle (you can do it on other game modes to )
you might join the spectator side but that is no problem it will count as a matched played .!
just spectate (or play if the game gives you the change) untill you got 7.
this method you will earn :
Played online battle 7 times
played endless battle 7 times
(and you can easy get observe 7 matches to bye spectating 7 times in endless battle )
and if you win a match it will count for those achievements too ofcourse :) !
Good luck !