For Desktop
Step 1) Login to your SportsEngine account
Step 2) Locate your team page
Step 3) Switch into Edit mode, click the 'Manage Team' button
Step 4) Select 'Schedule' from the left hand menu, click on the 'RSVPs' tab at the top of the page and then click into the game in question
Step 5) Once you're in the game you will have to option to message individuals or remind people to respond to the RSVP
For Mobile
Step 1) Login to your SportsEngine account
Step 2) Locate your team via the 'Favorites' tab
Step 3) Tap on 'Schedule' from the team page
Step 4) Scroll through the list of dates to find the event in question
Step 5) Player responses will appear below the event