I am using IOTstack which works with Docker, you will need to change your node-modules directory as needed.
Stop node-red container (I used Portainer CE)
Open linux terminal/Putty
cd /home/pi/IOTstack/volumes/nodered/data/node_modules/alexa-remote2
sudo mv alexa-remote.js alexa-remote.js.BAK
sudo mv alexa-wsmqtt.js alexa-wsmqtt.js.BAK
sudo mv package.json package.json.BAK
Download the latest from https://github.com/Apollon77/alexa-remote:
cd ~
mkdir alexatemp
cd alexatemp
git clone https://github.com/Apollon77/alexa-remote
cd alexa-remote
sudo cp alexa-remote.js /home/pi/IOTstack/volumes/nodered/data/node_modules/alexa-remote2
sudo cp alexa-wsmqtt.js /home/pi/IOTstack/volumes/nodered/data/node_modules/alexa-remote2
sudo cp package.json /home/pi/IOTstack/volumes/nodered/data/node_modules/alexa-remote2
cd ~
sudo rm -r alexatemp
exit