Here's how you can de-register from UPI:

1. Click on Vault 

2. Click on UPI settings under UPI section

3. Click on de-register

If you deregister from Tata Pay UPI, you will not be able make any transaction with Tata Pay UPI anymore

NOTE: You will not be able to deregister from Tata Pay UPI if you have a pending transaction or active mandate or you have done a transaction within last 7 days