@cmatheus22 in your gallery on the '>' button 'OnSelect' property you need to set a variable to allow them to appear and disappear the below allows the button to show on click and then hide on click
Set(ApproveButton,!ApproveButton)
The in the Visible Property of the button you need hidden add 'ApproveButton'
I have used the ApproveButton as an example you can name that what you want.
repeat the process for the other button naming that for example 'DeclineButton' so you'll end up with the below in the 'OnSelect' property of your gallery:
Set(ApproveButton,!ApproveButton); Set(DeclineButton,!DeclineButton)
I hope this helps?
Thanks
Jason