How To Return Hdd To Its Original Purchased State

I have a backup hdd that is currently has 4 partitions as shown below

What partition software can return it to a 1.8 TB to its original state as purchased

showing no partitions but instead 1.8 of unallocated space?

 

You can use Paragon Partition Manager Free to merge the partitions.
https://www.paragon-software.com/free/pm-express/#

 

You can use disk management in Windows, too,

Just to be sure "you only want one partition- with nothing except a clean formatted drive" ?
Then, you delete the last partition first, each time, (You should always do it like that to avoid problems ) and this will leave the complete drive empty (1862.9gb unallocated), then format it, give it a drive letter, or,keep it as G, as is.

 

Purchased state? wipe it with DBAN that would be like the 'purchased' state - blank unallocated.
Deleting all the partitions will still leave your data there, which is fine if your are keeping the drive for your use.