Restore contents of /etc/xrdp/startwm.sh

The original contents is here :

#!/bin/sh
# xrdp X session start script (c) 2015, 2017 mirabilos
# published under The MirOS Licence

if test -r /etc/profile; then
    . /etc/profile
fi

if test -r /etc/default/locale; then
    . /etc/default/locale
    test -z "${LANG+x}" || export LANG
    test -z "${LANGUAGE+x}" || export LANGUAGE
    test -z "${LC_ADDRESS+x}" || export LC_ADDRESS
    test -z "${LC_ALL+x}" || export LC_ALL
    test -z "${LC_COLLATE+x}" || export LC_COLLATE
    test -z "${LC_CTYPE+x}" || export LC_CTYPE
    test -z "${LC_IDENTIFICATION+x}" || export LC_IDENTIFICATION
    test -z "${LC_MEASUREMENT+x}" || export LC_MEASUREMENT
    test -z "${LC_MESSAGES+x}" || export LC_MESSAGES
    test -z "${LC_MONETARY+x}" || export LC_MONETARY
    test -z "${LC_NAME+x}" || export LC_NAME
    test -z "${LC_NUMERIC+x}" || export LC_NUMERIC
    test -z "${LC_PAPER+x}" || export LC_PAPER
    test -z "${LC_TELEPHONE+x}" || export LC_TELEPHONE
    test -z "${LC_TIME+x}" || export LC_TIME
    test -z "${LOCPATH+x}" || export LOCPATH
fi

if test -r /etc/profile; then
    . /etc/profile
fi

test -x /etc/X11/Xsession && exec /etc/X11/Xsession
exec /bin/sh /etc/X11/Xsession

The best way to get it , is either re-installing the xrdp package or if that's not possible for you , you can run the ISO image which you've installed the instance from , then install xrdp there and copy the file to your host.