Replace by fee, or RBF, lets you set a condition that allows a transaction be replaced by another which is identical in all aspects but has a higher miner fee assigned to it. This can be done multiple times while the transaction is unconfirmed.
RBF means you can accelerate a transaction and have it added to the next block. The feature can also be used to finalize a transaction.
RBF is enabled by default in Trezor Suite, meaning all transactions may have the associated fee 'bumped' at a later stage.
Increase the fee allocated to any unconfirmed RBF transaction by clicking Bump fee on the pending transaction in the Overview tab.
A dialog will open that lets you assign a new fee, which must be higher than the previous one. Click Replace transaction and then confirm the action on your Trezor.
💡 Learn more about replace by fee (RBF) on the Trezor knowledge base