Replace-by-fee (RBF) is a method that allows users to replace one version of an unconfirmed transaction with a different version of the transaction that pays a higher transaction fee. It was proposed in BIP125 and the initial implementation was released in Bitcoin Core 0.12.0.
RBF is now fully implemented in Trezor Suite as of version 21.2.2 and also has on-device support for Trezor Model T with firmware 2.3.5 and up as well as Trezor Model One with firmware 1.9.4 and up.
Choosing to bump a fee will open a dialog where a new custom fee can be set. This fee must be higher than the previous fee as it adds the difference to the total set in the previous transaction.
Once a new fee is selected in Suite, the transaction must be confirmed once again on Trezor, which will display the original transaction that is being replaced and the total fee you to be paid.
Some merchants, in particular those who would normally accept unconfirmed transactions, do not trust RBF-flagged transactions until a certain number of confirmations. In such cases, RBF can be turned off before paying them or an existing transaction can be finalized.
It is possible to use Replace-by-fee with Trezor device in Electrum. The original transaction can be replaced only if it was made using Electrum with the "Replace by fee" option on (Tools - Preferences - Replace by fee).