This document provides information on how to unjail a Validator jailed due to Down Time issues.

slashing unjail

If a Validator is Jailed, the Validator will not be able to sign blocks and will not be able to receive rewards as a result. Revive a Validator using the unjail transaction.
firmachaind tx slashing unjail \
--chain-id <chain-id> \
--from <keyname> \
--fees 20000ufct