Erased both partitions of my hard drive and want to merge them. They show up as two different disks so I cant choose the partition option External hard drive partitions showing as 2 different disks, can't merge or repartition. I have erased both and want to merge into one. 

EDIT: I have Reformatted both partitions to Mac OS Extended (Journaled) but still have the same problem. 

macOS Mojave Version 10.14.4
In Disk Utility go to the View menu and select 

"Show all devices." 

That should then show those two partitions under the "parent" physical drive mand allow you to repartition.