You can only set the device from which to share your location from the device that will share the users location.
As such, you’ll be able to choose your iPhone (if you have one) as the location sharing source from the Find My App installed on the iPhone. Similarly, to set your iPad as the source, you’ll use the Find My App installed on your iPad.
Assuming that all of your devices are signed-in to iCloud with the same AppleID, you can use the Find My App can on any of your devices to see which device is currently sharing your location.
More information here:
Find people and share your location with Find My - Apple Support