The most robust way to deliver new bacteria to your gut is with a gastro-resistant capsule (so it bypasses your stomach acid). Food will introduce it too; ferme

The most robust way to deliver new bacteria to your gut is with a gastro-resistant capsule (so it bypasses your stomach acid). Food will introduce it too; fermented foods contain more. Introducing the bacteria is only part of the problem though. If you want to have a diverse community of gut flora, you need to have a nutritionally balanced diet.