I partitioned my external hard drive about last year into 3 partitions, and now am trying to merge them together but I can't, I tried using diskpart , but did not succeed, its like the three partitions are like 3 different HDD in the harddisk, I also tried extend but didn't work, I deleted all the 3 partitions, but instead of showing me one partition as unallocated, it showed me 3 unallocated partition, pls how can I solve this problem

In disk part command there should be a command to delete partitions , send a screenshot of the failure if not if you can create a bootable Linux USB you can use Gparted

Can you could provide the screenshot of the disk management showing on your OS? But if you are Windows user, you can try some third-party software to merge all the unallocated space into the partition. Recommend the free aomei partition assistant, you can manage your hard drive with it.