To link your mobile number with your Voter ID, you need to fill out Form 8 and choose the option to updating the existing details. However, before updating, make sure that your name is the same on both your Aadhaar Card and Voter ID.
Steps to Link Mobile Number with Voter Card (EPIC Number) Online
Step 1: Go to the official CEO website https://voters.eci.gov.in
Step 2: On the homepage of the website, you have to click on "Login"

Step 3: To update mobile number you have to fill the Form 8 for correction in Existing Voter ID. Now you have to click on "Form 8" link shown after login.

Step 4: On the next page you have to select the Self option and enter your EPIC number and click on submit button.

Step 5: Then your details will be appeared and choose "Correction of Entries in Existing Electoral Roll"

Step 6: After that you have to enter the mobile number which you want to link with Voter ID under "Application for Correction of Entries in Existing Electoral Roll"

Step 7: Now you have to make a declaration and enter the captcha code then submit the Form 8

Check Mobile Number Voter ID Linking Application Status
After submitting Form 8, Voter’s can check the application status online to know if their name is added to the voter list.
Step 1: Open voters.eci.gov.in and login using your mobile number, password and OTP.
Step 2: Select Track Application Status from the dashboard.

Step 3: Enter your reference ID number and click on Submit button.
Step 4: Your voter registration status will appear on the screen.