Log in to your SolidCP. panel
Click on Accounts in POP/IMAP Email category:

Select mailbox you wish to edit:

Enter your new password or generate it by clicking on Generate Password:

Click on Save to save the changes.
Log in to your SolidCP. panel
Click on Accounts in POP/IMAP Email category:

Select mailbox you wish to edit:

Enter your new password or generate it by clicking on Generate Password:

Click on Save to save the changes.