To buy a phone on EMI, you must have a credit card with the appropriate Credit limit.
Then you can head to any online store like Flipkart and Amazon to buy your phone on EMI.
a. Open the App or website on your phone or PC
b. Then select the phone you want to buy and press buy now.
c. Select the Address and Tap on "Continue"
d. Select the "EMI" option as the mode of payment and Click on Continue.
e. Select your bank
f. Select the EMI time period from the options.
g. Enter your card details and make the payment.
You can see detailed product specifications here: OnePlus 7 Pro