First, try to download the detailed manual for your exact drive model from Seagate. Seagate is pretty good about publishing the detailed SATA/SCSI protocol documents for their devices. But only "pretty" good; parameters such as power saving modes may not be fully documented, in particular not for consumer devices. The reason behind that is that there is an expectation that consumers will not go down to the protocol level and modify device settings. The situation is different for enterprise devices (which are sold to Amazon/EMC/Google/HP/IBM/Microsoft/Oracle), where documentation about many more details is shared with the volume purchasers of the disks. By the way, little anecdote: For enterprise disks, about 99% of all disks are sold to ~10 customers, which are the companies on the list above and similar ones.
If you can get the detailed description of the power mode settings from the manuals, you can try to tune whether the disk goes to "sleep" (that includes unloading the heads). But it's quite possible that this is not even tunable, for two reasons: first, this disk may be intended for the consumer market, where there is no expectation that users will want to tune the behavior.
Second, it's very likely that Seagate has already adjusted the various drive parameters (head unload, spindle spindown, electronics sleep mode) both for optimal power usage and optimal disk lifetime. Modern disks wear out: Spindle bearings slowly lose lubricant, the spindle lubricant changes chemical composition (due to oxydation and partial distillation as they age), the lubricant that covers the platters also ages, and it interacts with the head (often leaving a thin film of lubricant on the head as the disk ages). There is a reason that disk manufacturers today specify a total annual IO throughput (typically 550 TB/year), and if one exceeds that, it voids the warranty. If you change the unload or spindown parameters, you might actually reduce the lifetime of your disk, and that may be why Seagate doesn't want you to do that (and doesn't document how), or makes it flat out impossible.
For an individual purchaser of a single disk, it may be impossible to get documentation about these technical details; on the other hand, for customers that buy hundreds of thousands of disks, working directly with Seagate engineering is common. If you insist on turning head unload off, you might want to try first finding documentation about it that's available to individuals, and then purchase a disk that can actually do it.