Once a transaction is confirmed on the blockchain, it is permanent. This is not limited to fomo. It applies to crypto as a whole.
Unlike traditional banking, there is no chargeback mechanism on the blockchain. There is no central authority that can reverse, cancel, or modify a confirmed transaction. If funds are sent to a wrong address or a wallet that does not exist, they cannot be recalled. If a token loses value after you bought it, there is no refund process. The transaction happened and the blockchain recorded it permanently.
Wallets created on fomo are non-custodial, which means your private keys your wallet. Funds are under your control at all times. No one at fomo can move, hold, or access your tokens. That same principle applies to why fomo cannot reverse a transaction on your behalf.