Hi @Manju Madhusoodhanannair(UST,IN) ,
Here is a similar thread: SharePoint Content DB exceed 200 GB. You could split the site collection into multiple site collections.each site collection should be in own content database.
You have to decide upon the usage and target department. Splitting the site collection will create a new URL for new site collection which may upset the users. When you split it to multiple site collections then you have to redevelop your coding if there is any. It is not an easy task but looks like this is the only options.
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