On Yay! there are 3 ways to delete a post.
・Select and delete posts (click here for how)
・Delete all posts in a batch (click here for how)
・Delete posts one at a time (see below for reference)
How to Delete a Post (One at a Time)
■Steps (For iOS and Android)
1. Display your post on the timeline or profile screen
2. Tap the ︙ button at the bottom right of the post
3. Tap Delete post on iOS or Delete for Android
4. A pop-up will be displayed, so tap Delete