Hi Anand,
Thank you for posting your query on Microsoft Q&A!
If you have access to a Global Administrator account which is linked to the original subscription you can re-gain access to it.
Login to portal.azure.com with the AzUser01 account and navigate to Entra ID - Properties - https://portal.azure.com/#view/Microsoft_AAD_IAM/ActiveDirectoryMenuBlade/~/Properties
Here you will see "Access management for Azure resources" where you can enable the User Access Administrator role for this account.
You might need to login again but you should now see the subscription listed under the Subscriptions blade - https://portal.azure.com/#view/Microsoft_Azure_Billing/SubscriptionsBladeV2
Here you can assign your AzUser01 account "Owner" permissions on the Free Trial subscription.
Let me know if you have any further queries, I would be happy to help.
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.
Kind Regards,
Donal