@0xfddfb30c4d1f010d08f3b5dd49ac2641f4601f67

Via bridge smart contracts. The tokens on other blockchains are not the same token, they are more like token certificates.
The bridges lock up the original tokens, and at the same time release/mint these certificate tokens of an equal amount on other blockchains. So the total amount of tokens and certificates in circulation remain the same.
These certificate tokens can be traded back to original tokens by bridging them back. I dont know if this process locks or burns or deletes the certificate token, but the effect is the same, the certificate tokens are taken out of circulation, as the originial tokens of an equal amount on their native blockchain are unlocked and released back to the circulating supply.

@0x69511d33ff4209618b47ffbcfb172c374024a57e Excellent explanation.