To switch to another account from your current account:
pwd /home/helper su projX Password: (password for account projX) whoami projX cd pwd /home/projX
The user helper switches to the account they have under the username projX and confirms this with the whoami command.
They then use the cd command to place themselves in the home directory for the account they have switched to. They can now work with the files and directories in this account in the usual way.