For the most part, it'll just need to build back up naturally. Probiotics really haven't shown a ton of benefit in large trials for certain issues, but maybe a little evidence that it might help some people with antibiotic associated diarrhea.

So generic probiotics might be beneficial, but apparently quality varies a lot between different brands, how long they've been on the shelf, shipping methods, etc. That being said it doesn't hurt to eat lots of fermented foods like yogurt, kimchi, saurkraut, kefir, etc.