DC Circuit breakers(DC MCB) last a long time so you should check your other options before deciding that issue is a faulty breaker. The breaker may need to be replaced if it trips very easily, doesn't trip when it should, can't be reset, is hot to the touch, or looks or smells burnt.
Friendly reminder. If you can't figure out the underlying issue or don't feel knowledgeable or experienced enough to do the repair yourself, call a professional electrician.
The following is how to replace your dc circuit breaker:
Shut off the branch circuit breakers one at a time.
Shut off the main circuit breaker.
Test all the wires with a voltage tester to make sure they're dead before proceeding.
Remove the panel cover.
Disconnect the wire of the breaker you're removing from the load terminal.
Carefully pry out the old breaker, paying careful attention to how it's positioned.
Insert the new breaker and push it into position.
Attach the circuit's wire to the load terminal. Strip a bit of insulation off the wires, if necessary.
Inspect the panel for any other problems. Tighten any loose terminals.
Replace the panel cover.
Turn on the main breaker.
Turn on the branch breakers one by one.
Test the breakers with a voltage tester to make sure everything is in order