Follow steps below how to make a p12 file for iOS :
Step 1 : Go to Apple Developer portal and click on Account
Step 2 : If you have an Apple Developer account, login, else create one by clicking on Create yours now
Step 3 : Click on Certificates, Identifiers & Profiles
Step 4 : Click the Add (+) button
Step 5 : Choose iOS Distribution (App Store and Ad Hoc)
Step 6 : Click on Continue
Step 7 : Click on Choose File to upload CSR file
Note : You can follow our tutorial "How to get CSR File?" to easily obtain the CSR file
Step 9 : Once done, click on Continue
Step 10 : Click on Download to download the certificate