how to modify x axis matplotlib code example

Example 1: 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)

Example 2: share x axis matplotlib

fig=plt.figure()
ax1 = plt.subplot(211)
ax2 = plt.subplot(212, sharex = ax1)