Follow below mentioned steps to add Billing account details in Google Developer Account to increase requests hit daily limit:
Step 1 : Go to Google Maps Platform
Step 2 : Click on Get Started
Step 3 : Click on Create Billing Account
Step 4 : Select country, and tick mark the check box to agree to Terms of Service
Step 5 : Click on Continue
Step 6 : Enter your Tax Information details, and click on Start My Free Trial