There seems to be a bit of confusion. The Captain / Co-Captain tournament is NOT a doubles tournament. It is single competition. Any player who is a captain or co-captain (or has been over the past league year) is eligible to participate. Changing your co-captain this past week will not make that person eligible to participate in this tournament. The Captain is the first person listed on your team roster. The Co-Captain is the second person listed on the team roster.
Go to Division Stats, choose 015/Foothill, go to schedule, scroll down to the list of teams and click on the map at the far right corner of any team that plays at The Mix.