A forfeited Texas LLC can't change its registered agent until it is reinstated, and reinstatement doesn't update the agent either. Here is the two step order that gets both fixed, and what is at risk while you wait.

When your registered agent resigns in Texas, the clock starts: the agent drops off after about 31 days, and the state can terminate your business if no replacement is named within roughly 90 days of its notice. Here is the timeline, the risk in the gap, and the one filing that fixes it.

Changing your registered agent in Texas comes down to one filing, Form 401, but it only goes through if your new agent has consented and your business is in good standing. Here's what gets it rejected.