Hi,
In the Azure portal, open Azure Active Directory, then open Users blade:
https://portal.azure.com/#view/Microsoft_AAD_UsersAndTenants/UserManagementMenuBlade/~/AllUsers
Click on the User account you would like to Disable. You may need to search for the account by entering text in the search box if you have more than 50 users.
Under Account status, click Edit.
Uncheck Account enabled, then click Save button.
If the above was useful please click Accept Answer.
Thanks.
-TP