You have 2 basic choices.
There are thread insert systems that might be able to save the crank. It depends on how much material was torn out, and whether the outer surface can be cleaned up and made flat, to accept the flange on the pedal. A decent shop should be able to do the job, or determine that it can't be.
The alternative is to buy and install a new crank arm.
Assuming it can be saved, the decision to save or replace would be based on the relative cost.
Lesson for the future, make a short list of various checks to be done before riding, or every few days. It should take but a minute or less and include a glance to make sure pedals are fully threaded in.
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