There are many different kinds of buckle of this type, so you will probably need to replace both parts (male and female) of the damaged buckle.
SU LIFE 2 Pack Side Release Buckles 1 inch / 25 mm
Forclaz 20 mm Backpack Quick Buckles 2-Pack
DYZD Multi-Size Plastic Buckle Repair Kit Quick
Buy BESPORTBLE 2Pcs Backpack Buckle, Strap Buckle, Quick Release Buckle, Replacement Fastening Buckle, Buckles for Straps, Plastic Clips for Straps
BESPORTBLE 2Pcs Backpack Buckle, Strap Buckle, Quick Release Buckle, Replacement Fastening Buckle, Buckles for Straps, Plastic Clips for Straps
Forclaz 38 mm Hiking Backpack Quick-Release Buckle
SU LIFE 2 Pack Side Release Buckles 1 inch / 25 mm
Forclaz 25 mm Quick-Release Backpack Buckles 2-Pack
Metal Hardware Accessories, Side Release Buckles
Package included: Pack of 4 Heavy Duty Stealth Side Release Buckles. Compatible with 1(25mm) webbing and straps. Buckle inner diameter: 1 inch No
DYZD Multi-Size Plastic Buckle Repair Kit Quick Release Buckles No Sewing Required Buckles for Backpack Bag (4pcs Black,25 mm)
Forclaz 25 mm Quick-Release Backpack Buckles 2-Pack
Metal Hardware Accessories, Side Release Buckles
Forclaz 38 mm Hiking Backpack Quick-Release Buckle
DYZD Multi-Size Plastic Buckle Repair Kit Quick
Buy BESPORTBLE 2Pcs Backpack Buckle, Strap Buckle, Quick Release Buckle, Replacement Fastening Buckle, Buckles for Straps, Plastic Clips for Straps
BESPORTBLE 2Pcs Backpack Buckle, Strap Buckle, Quick Release Buckle, Replacement Fastening Buckle, Buckles for Straps, Plastic Clips for Straps