A splint can sometimes work to support a fractured bone in your finger while it heals. However, a medical professional needs to address fractures.
Your doctor may need to order an X-ray to confirm a hairline fracture and to see if other treatment options are necessary. With your doctor's approval, you may be able to choose a splint from this list, or you may be advised to pick up a splint from a medical supply store that will offer the support that you need to heal properly.