2 notes at same place

Hello,
I don't succeed to put these 2 notes at same spot, like on the sheet you can (look yellow fluo on original partition and the one i'm trying to copy on MS)

Usually i simply click on the numbers "1-2-3-4" to do the trick but it doesn't work anymore when i add the dot at the note.

Do you guys know the answer to this problem ? I'm losing so much time on this, that's insane ahah.

Thank you and have a good evening.

PS : you'll see in original partition, strange notes in measure 8 (around first yellow), there is a mistake in the sheet for right hand ? It comes from a book, so i'd be surprised, i'm a novice, perhaps i don't understand something.