Hi Abu,
I guess that there is already an option in moodle to send email to users with welcome message and password during csv upload.
These are the required user identification fields:
username,firstname,lastname,email
Passwords
The "password" field is optional if the 'New user password' setting on the upload screen is set to "Create password if needed and send via email" but is required if the setting to "Field required in file".
Please try and hope this will work for you. You may check this link also - https://docs.moodle.org/34/en/Upload_usersThanks!
Suraj Kumar