change y tick label code example
Example: changing axis labels matplotlib
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
labels = [item.get_text() for item in ax.get_xticklabels()]
labels[1] = 'Testing'
ax.set_xticklabels(labels)
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
labels = [item.get_text() for item in ax.get_xticklabels()]
labels[1] = 'Testing'
ax.set_xticklabels(labels)