Hi @VeraRizvi ,
Could you please share a bit more about your scenario?
Do you want to set your custom wen page as Home page within your Portal?
Based on the needs that you mentioned, I think it is not necessary to change the Homepage in your Portal into another web page, instead, you could made some customization within this Home page directly.
Please check and see if the following article would help in your scenario:
https://carldesouza.com/how-to-create-and-customize-a-custom-power-apps-portal-for-your-organization/
If you just want to change the Home page into another customer web page, you need to firstly to delete the Home page from the Web Pages tab within your Portal management.

Then edit your custom web page, then set the Parent Page field to blank, set the Partial URL field to "/" as below:

after that, edit other pages in your Portal, then modify the Parent Page field and Partial URL field value, make them act as child pages under your custom Home page.
Best regards,