A rent credit is a state credit so if you need to amend a return, you have to amend the state return. Or you might be able to go to the state's web site to work on the rent credit. You have not mentioned what state you are asking about so we cannot provide specific details for you.
To amend only a state return:
https://ttlc.intuit.com/questions/2824532-i-need-to-amend-my-state-return
https://ttlc.intuit.com/questions/3827521-can-i-efile-an-amended-state-return
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**