It's not clear where you need to make this change. But the following article may help: How to change the Logo in the Banner?
If this posting does not resolve your issue, please provide further details and possibly a screenshot to clarify your needs.
Greetings shalini visveswaraiya,
Following up with you on the original question posted here, can you please indicate if the recommendations given by either Sharon, Varathan, or Polina answered this for you?
If any of these posts adequately answered your question, please mark the reply as the "Correct Answer."
Or, if you are still unresolved on your original question, let us know and we can continue troubleshooting this with you. This feedback is a key step toward ensuring Community users with a similar issue are able to locate the information they need.