You can Aadhaar Link to two type step
1. First if when are you return file fill up during one have option avail for Aadhaar number for putting then you can submit Aadhaar Number. After finally submitting time for verification with otp now successfully update your Aadhaar number in income tax.
Also read: How to create Account For income tax
:How to return file Income Tax India
2. Second you can go to directly on official website of Income Tax department. and fill the all details then sumbit after verification with opt then your Aadhaar linked successfully.
If any problems face during liking Aadhaar Number you can comment inbox I will try to help.