I don't know how to load it
Like HRL says "Load the battery to 1/2 the cold cranking amp specification for 20 seconds, or find someone who can".
I've always used a general rule of thumb that battery needs at least 1 CCA per cubic inch of motor.
If you feel like an investment, or if a local shop cannot load it for you, most Farm and Ranch stores, or an O'rielly's can sell you one of these:
https://www.schumacherelectric.com/products/battery-load-tester/
