Go to virtual box installation directory and execute the below command to change UUID of an existing .vdi file
C:\Program Files\Oracle\VirtualBox>VBoxManage.exe internalcommands sethduuid E:\SOM\SOM.vdi
UUID changed to: 257998ef-0b52-4b69-bda7-70b88b73236b
C:\Program Files\Oracle\VirtualBox>
Now after changing the UUID, open Virtual Box and select the settings for the image and select the .vdi file instead of the old .vdi file
C:\Program Files\Oracle\VirtualBox>VBoxManage.exe internalcommands sethduuid E:\SOM\SOM.vdi
UUID changed to: 257998ef-0b52-4b69-bda7-70b88b73236b
C:\Program Files\Oracle\VirtualBox>
Now after changing the UUID, open Virtual Box and select the settings for the image and select the .vdi file instead of the old .vdi file