Waving your hand over the phone's top to switch to external speaker mode during calls.
Waving your hand to switch to external speaker on Vivo Y55s as follows:
Step 1: Go to 'Settings' and select 'Smart Motion Control'.

Select 'Smart Motion Control'.
Step 2: Choose 'Intelligent Calling'.

Choose 'Intelligent Calling'.
Step 3: Turn on 'Wave to Use Hands-Free Mode'.

Enable 'Wave to Activate Hands-Free Mode'.
With that, your setup process is complete. Wishing you all success!
