Problems with Node-Red flow credentials

I recently installed Node-Red with their script command ```
bash <(curl -sL https://raw.githubusercontent.com/node-red/linux-installers/master/deb/update-nodejs-and-nodered)



"Welcome to Node-RED
===================

30 Sep 20:03:51 - [info] Node-RED version: v1.1.3
30 Sep 20:03:51 - [info] Node.js  version: v12.18.4
30 Sep 20:03:51 - [info] Linux 5.4.51-v7+ arm LE
30 Sep 20:03:52 - [info] Loading palette nodes
30 Sep 20:03:54 - [info] Settings file  : /home/pi/.node-red/settings.js
30 Sep 20:03:54 - [info] Context store  : 'default' [module=memory]
30 Sep 20:03:54 - [info] User directory : /home/pi/.node-red
30 Sep 20:03:54 - [warn] Projects disabled : editorTheme.projects.enabled=false
30 Sep 20:03:54 - [info] Flows file     : /home/pi/.node-red/flows_raspberrypi.json
30 Sep 20:03:54 - [info] Creating new flow file
30 Sep 20:03:54 - [warn]

---------------------------------------------------------------------
Your flow credentials file is encrypted using a system-generated key.

If the system-generated key is lost for any reason, your credentials
file will not be recoverable, you will have to delete it and re-enter
your credentials.

You should set your own key using the 'credentialSecret' option in
your settings file. Node-RED will then re-encrypt your credentials
file using your chosen key the next time you deploy a change.
---------------------------------------------------------------------

30 Sep 20:03:54 - [info] Starting flows
30 Sep 20:03:54 - [info] Started flows
30 Sep 20:03:54 - [error] Unable to listen on http://127.0.0.1:1880/
30 Sep 20:03:54 - [error] Error: port in use"

Any suggestions how to solve it?

No issues there except the port is being used by some other device. Try starting with a different port,
https://nodered.org/docs/getting-started/local#command-line-usage.
Or set the port in the settings js,
https://nodered.org/docs/user-guide/runtime/configuration

Which is probably another instance of Node-RED. So before going straight to changing the port, the question is whether they want two instances of node-red running or not.

Probably.