If you disconnected an account, you will see the account greyed out at the end of your account list in the group 'Disconnected'.
To restore a disconnected account, please proceed as follows:
'Accounts' > 'select account' > 'Select the three points next to the contoname' > 'Settings' > 'Disconnect Account' > 'OFF'
The account is now displayed as asctive again in your account list and the group, it belonged to.
If you have hidden an account, it will no longer appear in the account list.
To display a hidden account again, please proceed as follows:
'Settings' > 'Select credentials' > 'Select Account'> 'Hide Account' >'OFF'