Hello Saurabh,
the HANA trial instance on the HCP trial account has some limitations, because the system is shared with different users. One of the limitations is that you cannot import delivery units. So you will not be able to do the openSAP exercise on the HCP HANA trial instance.
If you wanna do it, you need your own HANA. Either a sandbox system of your company or a free SAP HANA developer edition supplied by SAPs Cloud Appliance Library (SAP HANA Enterprise Cloud / Cloud Appliance Library). In the second case you need to consider that you do not have to pay any license costs for the HANA developer edition, but you will be charged for the AWS or Azure runtime.
Regarding the question which rights are necessary to import DUs: That is already answered by Tom Jung in the discussion you linked above.
Best Regards,
Florian