Start DiskPart by opening Start menu and typing in diskpart in the search. After giving DiskPart permission to start with administrative privileges, you will be in a console window with DISKPART>prompt.
Deleting partitions
Type LIST DISK to find out what disk you need to change. Note that you are looking for a disk with the same number as in the Disk Management tool, so in OP’s case, it’s Disk 1.
Next you need to select the disk you wish to work on. Type SELECT DISK 1. Make sure the correct disk is selected by typing LIST DISK again.
Now, you need to select the partition you wish to remove. Type LIST PARTITION to see a list of all partitions. To select the first one, type SELECT PARTITION 1.
To remove the partition, type DELETE PARTITION.
Creating partitions
To create a partition, you can either proceed by using the Disk Management tool, or type CREATE PARTITION PRIMARY. This creates a partition that fills the free space. If you wish to create a partition of specific size, you need to type CREATE PARTITION PRIMARY SIZE=NNN where NNN is the partition size in MB.
You can get more information about the various options by typing HELP CREATE PARTITION and/or HELP CREATE PARTITION PRIMARY.
Exiting DiskPart
Either type EXIT or press Ctrl+C.
Additional notes
While this works for many SD cards (and other media), for SD cards specifcially, it is recommended to use SD formatter from SD Association. It will not only remove all partitions but ensure that any content security-related parts of the card are left intact.
Although not being asked, this method may not work for USB sticks. I have ‘bricked’ USB sticks by partitioning them on Linux or writing ISO images to them, and to date, I haven’t found a way to fix them.
https://superuser.com/questions/485756/how-do-i-repartition-an-sdhc-card-in-windows