old_customers = {'3492': 'Harry', '9872': 'Emerson',
             '7829': 'Aiman'}
new_customers = {'3672': 'Safa', '2910': 'Saim', 
             '6512': 'Rabi'}
merged_dict = {}
for key, value in old_customers.items():
    merged_dict[key] = value
for key, value in new_customers.items():
    merged_dict[key] = value
print(merged_dict)