The Learning Rate is a concept related to the training of Handwritten Text Recognition models. It defines the increment from one epoch to another, so how fast the training will proceed. With a higher value, the CER will go down faster. BUT: the higher the value, the higher the risk, that details are overlooked. This value is adaptive and will be adjusted automatically. The training is influenced though by the value it is started with. You can go with the default setting here.