Hi. If you want to change your mobile number in apna app, please follow these steps:
Step 1: Go to the Profile page of the app.

Step 2: Click on the 3 dots.

Step 3: Click on the 'Logout' option.

Step 4: Select the 'Delete profile' option from the top right corner of the screen
Please note: All current info and data will be deleted along with your current profile.
Step 5: Once that is done, please log in with your new phone number and make your profile/ID again.
Good luck!