If your club allows players to schedule their own matches with their opponents, then you and your teammate are responsible for making sure you play all your matches against other teams in your division.
To get in contact with your opponents:
Once a round has been launched by the club, go to the league in the app -> upcoming. This view shows you all your upcoming matches, no matter if they are already scheduled or not. Non-scheduled matches have a ”plan your match” button where you can message with the other participants of that specific match.
Before suggesting days and times, make sure you check available match-times defined by the club for your league in ”book your match”. You can click in to that flow to see the dates, times, courts, without actually booking in the match.