Tap the days you can't play; auto-fill skips you and your leader can see it.
Open My schedule from the sidebar and tap any day you can't play — it turns red with a line through it. Tap again to clear it.
You only ever mark the days you're away; a blank calendar means available. When a leader auto-fills the rota, anyone marked away that Sunday is skipped. Leaders and admins can see everyone's block-outs. It works offline — taps sync when you reconnect.