It's a green app with a white "X" on it. If you're logged into your Microsoft account, doing so will open the last tab you had open. If you aren't logged in, tap Sign in when prompted and enter your Microsoft account email address and password, then tap Sign in followed by Start using Excel. It's in the bottom-left corner of the screen. If Excel opened to a document, first tap File in the top-left corner of the screen, then tap Open instead of Open other workbooks. This will open the OneDrive save location. Doing so will open it in Excel. Depending on where in OneDrive the document resides, you may have to tap through some folders to open it. It's the person-shaped button at the top of the screen. Doing so will prompt a drop-down menu. Don't tap the person-shaped icon in the far-right corner of the screen--that's your profile button. This option is near the top of the drop-down menu. It's to the right of a user's name. Doing so will remove your selected user from the "share" list. After you've uninvited all users from the document, the document will no longer be shared with anyone.

TL;DR in Indonesian:
Buka Excel. Ketuk Open other workbooks. Ketuk OneDrive - Personal. Ketuk dokumen yang ingin dihentikan pembagiannya. Ketuk ikon "Share". Ketuk Manage. Ketuk ⋮. Ketuk Stop sharing. Hentikan pembagian dokumen dengan semua pengguna lain.