Dear Dudimetla Ramalingaiah
Good morning! Thank you for posting your query in our community.
According to your description, you encountered some issue while uploading html in SharePoint Online.
However, since community moderators here focus on out-of-box features in SharePoint Online, we suggest that you post html programming questions to Questions - Microsoft Q&A using the sharepoint development tag, along with any other relevant tags.
Here is a similar thread I found for your reference and you may consider post a new thread based on your own scenario to get dedicated support from engineers in there. How to create/convert html page to Master Page on sharepoint online ( office 365 ) - Microsoft Q&A
Meanwhile, I will keep this thread open, so that other MVPs or members in our community can share their ideas with this thread.
Thank you for your patience and understanding. Hope you have a nice day!
Sincerely
Mia | Microsoft Community Moderator