You can't change the location. The Snapshot is created in the same datastore where the disk is located. You would need to change the disk to another datastore. 

Exactly what Wes said if you have datastore space issues move the VM to one with more space.

Actually there is a way to change the location where snapshots are stored. But this is not done inside Veeam. Instead you need to change the working directory for each VM within the configuration (VMX). I wouldn't recommend to do so as a misconfiguration could take your VMs offline. But for a single VM or only temporary you can go this way.

https://knowledge.broadcom.com/external/article/314378/creating-snapshots-in-a-different-locati.html

During the job Veeam will instruct VMware to take the snapshot, so there’s nothing you can change from the Veeam side. However, as Max mentioned, you can modify the VMX file to save the snapshot disk to a different datastore but this is risky and not recommended.

If a VM needs more space, the correct approach is to provision it properly,  either by allocating additional space or migrating the VM to a datastore with sufficient capacity. Make sure to maintain at least 20–30% free space relative to the VM’s disk size on the datastore. This buffer helps prevent snapshot failures or unexpected crashes.