how do i restore my iphone 6s plus without a home button

if it were not asking for recovery mode and you had lock screen notifications on, you could send yourself a mail or message and try to open it. It would put you onto the passcode

You could have then activated assistive touch with the dummy home button but at this stage I am pretty sure you need the home button itself to put it into DFU mode.

The 6S plus has a home button so presumably you mean it is broken?

You cannot restore it until it has been repaired