To find it, you'll likely need to:
1. Consult your owner's manual: This is the best place to start. It should have a diagram showing the location of fuses and relays, and the flasher unit is often near these.
2. Look for a fuse block: The flasher unit is often mounted on or near the fuse block.
3. Remove some interior trim panels: You may need to carefully remove some panels under the dash to access the area where the flasher unit is located. Be gentle to avoid breaking any clips.
If you can't find it after searching these areas, a search online for "1997 Chevy Astrovan flasher unit location" along with images may help. You can also consult a mechanic or auto parts store for assistance.