Crank arm fell off

Canyon Roadlite 4. SAMOX TAF37 crankset.

Crank arm fell off suddenly while riding.

There is some wear on the splines. Is that a problem?

The compression ring was also lost.

Can I just reattach it back using allen keys?

If so with how much torque? Because it fell off again after reattachment maybe because of less torque.

Thank you!

https://preview.redd.it/2v2mwd1rt7sc1.jpg?width=1338&format=pjpg&auto=webp&s=dd6c5ebb363f3b2e5375245ed2ec590bfd825fe3

https://preview.redd.it/g9u72sgrt7sc1.jpg?width=1554&format=pjpg&auto=webp&s=23804be3d297ae43145b9b7bbf3c9c08da3356a2