To login to the e-mail accounts you'll need to go here, add @ysgolplasmawr.cymru and use the same password.
Students Hwb credentials are usually reset in year 7 and their details will have been sent to their school e-mail, if they login to their school e-mail and search for 'Manylion Hwb' they should find them, please be sure to check the 'Deleted items' folder!
Please be aware that both Hwb and ysgolplasmawr.cymru accounts are on the Microsoft 365 platform, therefore users should be logged out of one before attempting to login to the other.
You can either use different browsers for the different accounts or setup profiles within a browser to keep the accounts/cookies separate.
If you are still in need of help please contact the school as above.